diff --git a/components/email/__tests__/thread-list-item.test.tsx b/components/email/__tests__/thread-list-item.test.tsx
index f9b312e39..4b3f6d249 100644
--- a/components/email/__tests__/thread-list-item.test.tsx
+++ b/components/email/__tests__/thread-list-item.test.tsx
@@ -53,7 +53,7 @@ describe('ThreadListItem tag badge', () => {
       mailLayout: 'split',
     });
     useEmailStore.setState({
-      selectedEmailIds: new Set<string>(),
+      selectedEmailKeys: new Set<string>(),
       selectedMailbox: 'inbox',
     });
   });
@@ -126,7 +126,7 @@ describe('ThreadListItem multi-message thread', () => {
       mailLayout: 'split',
     });
     useEmailStore.setState({
-      selectedEmailIds: new Set<string>(),
+      selectedEmailKeys: new Set<string>(),
       selectedMailbox: 'inbox',
     });
   });
@@ -187,7 +187,7 @@ describe('ThreadListItem row content', () => {
       mailLayout: 'split',
     });
     useEmailStore.setState({
-      selectedEmailIds: new Set<string>(),
+      selectedEmailKeys: new Set<string>(),
       selectedMailbox: 'inbox',
     });
   });
@@ -226,8 +226,8 @@ describe('ThreadListItem shift-range avatar selection', () => {
     // Selection mode active, with the anchor on e1.
     useEmailStore.setState({
       emails: [e1, e2, e3],
-      selectedEmailIds: new Set(['e1']),
-      lastSelectedEmailId: 'e1',
+      selectedEmailKeys: new Set(['e1']),
+      lastSelectedEmailKey: 'e1',
       selectedMailbox: 'inbox',
     });
 
@@ -237,7 +237,7 @@ describe('ThreadListItem shift-range avatar selection', () => {
       avatar.dispatchEvent(new MouseEvent('click', { bubbles: true, shiftKey: true }));
     });
 
-    const selected = useEmailStore.getState().selectedEmailIds;
+    const selected = useEmailStore.getState().selectedEmailKeys;
     expect(selected.has('e1')).toBe(true);
     expect(selected.has('e2')).toBe(true); // the row in between got filled in
     expect(selected.has('e3')).toBe(true);
@@ -256,7 +256,7 @@ describe('ThreadListItem row tint', () => {
       tintListRowsByTag: true,
     });
     useEmailStore.setState({
-      selectedEmailIds: new Set(['email-1']),
+      selectedEmailKeys: new Set(['email-1']),
       selectedMailbox: 'inbox',
     });
   });
diff --git a/components/email/email-list.tsx b/components/email/email-list.tsx
index 71ef9e256..37bb72a15 100644
--- a/components/email/email-list.tsx
+++ b/components/email/email-list.tsx
@@ -88,7 +88,7 @@ export function EmailList({
   const tSpam = useTranslations('email_viewer.spam');
   const { client } = useAuthStore();
   const {
-    selectedEmailIds,
+    selectedEmailKeys,
     selectAllEmails: _selectAllEmails,
     clearSelection,
     batchMarkAsRead,
@@ -227,7 +227,7 @@ export function EmailList({
     </div>
   );
 
-  const hasSelection = selectedEmailIds.size > 0;
+  const hasSelection = selectedEmailKeys.size > 0;
 
   const handleBatchMarkAsRead = async (read: boolean) => {
     if (!client || isProcessing) return;
@@ -243,7 +243,7 @@ export function EmailList({
     if (!client || isProcessing) return;
     setIsProcessing(true);
     try {
-      const emailIds = Array.from(selectedEmailIds);
+      const emailIds = Array.from(selectedEmailKeys);
       await batchUndoSpam(client, emailIds);
       const { toast } = await import('sonner');
       toast.success(tSpam('toast_not_spam_batch', { count: emailIds.length }));
@@ -266,8 +266,8 @@ export function EmailList({
         ? t('permanent_delete_confirm_title')
         : t('batch_actions.delete_confirm_title'),
       message: isInTrash
-        ? t('permanent_delete_confirm_batch_message', { count: selectedEmailIds.size })
-        : t('batch_actions.delete_confirm_message', { count: selectedEmailIds.size }),
+        ? t('permanent_delete_confirm_batch_message', { count: selectedEmailKeys.size })
+        : t('batch_actions.delete_confirm_message', { count: selectedEmailKeys.size }),
       confirmText: isInTrash
         ? t('permanent_delete')
         : t('batch_actions.delete'),
@@ -391,7 +391,7 @@ export function EmailList({
         <div className="px-4 py-2 border-b bg-accent/30 border-border flex items-center justify-between">
           <div className="flex items-center gap-2 animate-in fade-in slide-in-from-left-3 duration-300">
             <span className="text-sm font-medium text-foreground">
-              {t('batch_actions.selected_messages', { count: selectedEmailIds.size })}
+              {t('batch_actions.selected_messages', { count: selectedEmailKeys.size })}
             </span>
           </div>
           <div className="flex items-center gap-1 animate-in fade-in slide-in-from-right-3 duration-300">
@@ -629,8 +629,8 @@ export function EmailList({
           mailboxes={mailboxes}
           selectedMailbox={selectedMailbox}
           currentMailboxRole={effectiveMailboxRole}
-          isMultiSelect={selectedEmailIds.has(contextMenuEmail.id)}
-          selectedCount={selectedEmailIds.size}
+          isMultiSelect={selectedEmailKeys.has(contextMenuEmail.id)}
+          selectedCount={selectedEmailKeys.size}
           onReply={() => onReply?.(contextMenuEmail!)}
           onReplyAll={() => onReplyAll?.(contextMenuEmail!)}
           onForward={() => onForward?.(contextMenuEmail!)}
@@ -660,7 +660,7 @@ export function EmailList({
           onBatchMoveToMailbox={(mailboxId) => client && batchMoveToMailbox(client, mailboxId)}
           onBatchMarkAsSpam={async () => {
             if (client) {
-              const emailIds = Array.from(selectedEmailIds);
+              const emailIds = Array.from(selectedEmailKeys);
               try {
                 await batchMarkAsSpam(client, emailIds);
                 const { toast } = await import('sonner');
@@ -675,7 +675,7 @@ export function EmailList({
           }}
           onBatchUndoSpam={async () => {
             if (client) {
-              const emailIds = Array.from(selectedEmailIds);
+              const emailIds = Array.from(selectedEmailKeys);
               try {
                 await batchUndoSpam(client, emailIds);
                 const { toast } = await import('sonner');
diff --git a/components/email/thread-email-item.tsx b/components/email/thread-email-item.tsx
index 24c97d7e7..ca6b99aaf 100644
--- a/components/email/thread-email-item.tsx
+++ b/components/email/thread-email-item.tsx
@@ -45,9 +45,9 @@ export function ThreadEmailItem({
   // header pools them, so without this they disappear on the way in.
   const tagIds = sortTagIds(getEmailTagIds(email.keywords));
   const sender = email.from?.[0];
-  const { selectedMailbox, selectedEmailIds, toggleEmailSelection, selectRangeEmails, clearSelection } = useEmailStore();
+  const { selectedMailbox, selectedEmailKeys, toggleEmailSelection, selectRangeEmails, clearSelection } = useEmailStore();
   const density = useSettingsStore((state) => state.density);
-  const isChecked = selectedEmailIds.has(email.id);
+  const isChecked = selectedEmailKeys.has(email.id);
 
   const { dragHandlers, isDragging } = useEmailDrag({
     email,
@@ -73,18 +73,18 @@ export function ThreadEmailItem({
 
   const handleCheckboxClick = (e: React.MouseEvent) => {
     e.stopPropagation();
-    toggleEmailSelection(email.id);
+    toggleEmailSelection(email);
   };
 
   const handleClick = (e: React.MouseEvent) => {
     if (e.ctrlKey || e.metaKey) {
       e.preventDefault();
-      toggleEmailSelection(email.id);
+      toggleEmailSelection(email);
     } else if (e.shiftKey) {
       e.preventDefault();
-      selectRangeEmails(email.id);
+      selectRangeEmails(email);
     } else {
-      if (selectedEmailIds.size > 0) clearSelection();
+      if (selectedEmailKeys.size > 0) clearSelection();
       onClick?.();
     }
   };
@@ -118,7 +118,7 @@ export function ThreadEmailItem({
     >
       <div className="flex items-start gap-3">
         {/* Checkbox - only visible when in selection mode */}
-        {selectedEmailIds.size > 0 && (
+        {selectedEmailKeys.size > 0 && (
           <button
             onClick={handleCheckboxClick}
             className={cn(
diff --git a/components/email/thread-list-item.tsx b/components/email/thread-list-item.tsx
index 19ac9c4da..539d1b2a7 100644
--- a/components/email/thread-list-item.tsx
+++ b/components/email/thread-list-item.tsx
@@ -165,7 +165,7 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
     const isPinned = email.keywords?.['$pinned'] === true;
     const isAnswered = email.keywords?.$answered;
     const isForwarded = email.keywords?.$forwarded;
-    const { selectedMailbox, mailboxes, selectedEmailIds, toggleEmailSelection, selectRangeEmails, clearSelection, isUnifiedView, unifiedRole } = useEmailStore();
+    const { selectedMailbox, mailboxes, selectedEmailKeys, toggleEmailSelection, selectRangeEmails, clearSelection, isUnifiedView, unifiedRole } = useEmailStore();
     // In Sent/Drafts folders, show recipient instead of sender (which is always
     // "me"). In aggregate role-views the selected mailbox is virtual → fall back
     // to the unified role so junk-contextual UI and avatar hiding work.
@@ -187,7 +187,7 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
     const account = email.accountId ? getAccountById(email.accountId) : undefined;
     const accountColor = account?.avatarColor;
     const accountDescription = describeAccount(email.accountLabel, account);
-    const isChecked = selectedEmailIds.has(email.id);
+    const isChecked = selectedEmailKeys.has(email.id);
     const isMobile = useUIStore((state) => state.isMobile);
     // The horizontal one-line "focus" layout doesn't fit on narrow screens; fall back to multi-line on mobile.
     const isFocusedMailLayout = mailLayout === 'focus' && !isMobile;
@@ -267,9 +267,9 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
     const handleCheckboxClick = (e: React.MouseEvent) => {
       e.stopPropagation();
       if (e.shiftKey) {
-        selectRangeEmails(email.id);
+        selectRangeEmails(email);
       } else {
-        toggleEmailSelection(email.id);
+        toggleEmailSelection(email);
       }
     };
 
@@ -281,12 +281,12 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
       if (swipeEnabled && consumeTap()) { return; }
       if (e.ctrlKey || e.metaKey) {
         e.preventDefault();
-        toggleEmailSelection(email.id);
+        toggleEmailSelection(email);
       } else if (e.shiftKey) {
         e.preventDefault();
-        selectRangeEmails(email.id);
+        selectRangeEmails(email);
       } else {
-        if (selectedEmailIds.size > 0) clearSelection();
+        if (selectedEmailKeys.size > 0) clearSelection();
         onClick();
       }
     };
@@ -348,7 +348,7 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
           style={{ gap: 'var(--density-item-gap)', paddingBlock: 'var(--density-item-py)', transform: swipeEnabled && offsetX ? `translateX(${offsetX}px)` : undefined, transition: swipeEnabled && offsetX === 0 ? 'transform 200ms ease-out' : undefined }}
         >
           {/* Checkbox - only for extra-compact density (no avatar) while in selection mode */}
-          {density === 'extra-compact' && selectedEmailIds.size > 0 && (
+          {density === 'extra-compact' && selectedEmailKeys.size > 0 && (
             <button
               onClick={handleCheckboxClick}
               role="checkbox"
@@ -641,7 +641,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
       ? formatDateTime(latestEmail.scheduledSendAt, timeFormat)
       : null;
 
-    const { selectedMailbox, mailboxes, selectedEmailIds, toggleEmailSelection, selectRangeEmails, clearSelection, isUnifiedView, unifiedRole } = useEmailStore();
+    const { selectedMailbox, mailboxes, selectedEmailKeys, toggleEmailSelection, selectRangeEmails, clearSelection, isUnifiedView, unifiedRole } = useEmailStore();
     const showSourceFolder = isUnifiedView && !!latestEmail.sourceFolder;
     const getAccountById = useAccountStore((state) => state.getAccountById);
     const threadAccount = latestEmail.accountId ? getAccountById(latestEmail.accountId) : undefined;
@@ -688,7 +688,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
     const isSelected = selectedEmailId === latestEmail.id ||
       thread.emails.some(e => e.id === selectedEmailId);
 
-    const isChecked = thread.emails.some(e => selectedEmailIds.has(e.id));
+    const isChecked = thread.emails.some(e => selectedEmailKeys.has(e.id));
 
     if (emailCount === 1) {
       return (
@@ -717,8 +717,8 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
 
     // Toggle selection for all emails in this thread.
     const toggleThreadSelection = () => {
-      const allSelected = thread.emails.every(em => selectedEmailIds.has(em.id));
-      const newSelection = new Set(selectedEmailIds);
+      const allSelected = thread.emails.every(em => selectedEmailKeys.has(em.id));
+      const newSelection = new Set(selectedEmailKeys);
       thread.emails.forEach(em => {
         if (allSelected) {
           newSelection.delete(em.id);
@@ -726,13 +726,13 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
           newSelection.add(em.id);
         }
       });
-      useEmailStore.setState({ selectedEmailIds: newSelection, lastSelectedEmailId: latestEmail.id });
+      useEmailStore.setState({ selectedEmailKeys: newSelection, lastSelectedEmailKey: latestEmail.id });
     };
 
     const handleThreadCheckboxClick = (e: React.MouseEvent) => {
       e.stopPropagation();
       if (e.shiftKey) {
-        selectRangeEmails(latestEmail.id);
+        selectRangeEmails(latestEmail);
         return;
       }
       toggleThreadSelection();
@@ -742,12 +742,12 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
       if (e.ctrlKey || e.metaKey) {
         e.preventDefault();
         // Ctrl+Click: toggle selection for all thread emails
-        thread.emails.forEach(em => toggleEmailSelection(em.id));
+        thread.emails.forEach(em => toggleEmailSelection(em));
         return;
       }
       if (e.shiftKey) {
         e.preventDefault();
-        selectRangeEmails(latestEmail.id);
+        selectRangeEmails(latestEmail);
         return;
       }
 
@@ -760,7 +760,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
       if (target.closest('[data-expand-toggle]')) {
         onToggleExpand();
       } else {
-        if (selectedEmailIds.size > 0) clearSelection();
+        if (selectedEmailKeys.size > 0) clearSelection();
         if (!isExpanded) {
           onCollapseAllThreads?.();
           onToggleExpand();
@@ -812,7 +812,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
             style={{ gap: 'var(--density-item-gap)', paddingBlock: 'var(--density-item-py)' }}
           >
             {/* Checkbox for thread selection - only for extra-compact density (no avatar) while in selection mode */}
-            {density === 'extra-compact' && selectedEmailIds.size > 0 && (
+            {density === 'extra-compact' && selectedEmailKeys.size > 0 && (
               <button
                 onClick={handleThreadCheckboxClick}
                 role="checkbox"
diff --git a/components/mail/mail-app.tsx b/components/mail/mail-app.tsx
index dc821d1d6..19c37a6d6 100644
--- a/components/mail/mail-app.tsx
+++ b/components/mail/mail-app.tsx
@@ -338,7 +338,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     newEmailNotification,
     selectEmail,
     selectMailbox,
-    selectedEmailIds,
+    selectedEmailKeys,
     selectAllEmails,
     clearSelection,
     toggleEmailSelection,
@@ -703,7 +703,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     },
     onArchive: async () => {
       if (isScheduledView) return;
-      if (selectedEmailIds.size > 0 && client) {
+      if (selectedEmailKeys.size > 0 && client) {
         try {
           await batchArchive(client);
         } catch (error) {
@@ -719,7 +719,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     },
     onDelete: async () => {
       if (isScheduledView) return;
-      if (selectedEmailIds.size > 0 && client) {
+      if (selectedEmailKeys.size > 0 && client) {
         const currentMailbox = mailboxes.find(m => m.id === selectedMailbox);
         const isInTrash = currentMailbox?.role === 'trash';
         const isInJunk = currentMailbox?.role === 'junk';
@@ -730,8 +730,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
             ? t('email_list.permanent_delete_confirm_title')
             : t('email_list.batch_actions.delete_confirm_title'),
           message: permanent
-            ? t('email_list.permanent_delete_confirm_batch_message', { count: selectedEmailIds.size })
-            : t('email_list.batch_actions.delete_confirm_message', { count: selectedEmailIds.size }),
+            ? t('email_list.permanent_delete_confirm_batch_message', { count: selectedEmailKeys.size })
+            : t('email_list.batch_actions.delete_confirm_message', { count: selectedEmailKeys.size }),
           confirmText: permanent
             ? t('email_list.permanent_delete')
             : t('email_list.batch_actions.delete'),
@@ -750,7 +750,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     onMarkAsUnread: async () => {
       if (isScheduledView) return;
       if (!client) return;
-      if (selectedEmailIds.size > 0) {
+      if (selectedEmailKeys.size > 0) {
         await batchMarkAsRead(client, false);
       } else if (selectedEmail) {
         await markAsRead(client, selectedEmail.id, false);
@@ -759,7 +759,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     onMarkAsRead: async () => {
       if (isScheduledView) return;
       if (!client) return;
-      if (selectedEmailIds.size > 0) {
+      if (selectedEmailKeys.size > 0) {
         await batchMarkAsRead(client, true);
       } else if (selectedEmail) {
         await markAsRead(client, selectedEmail.id, true);
@@ -773,8 +773,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
       // is a no-op there too.
       if (['sent', 'drafts', 'scheduled'].includes(currentMailbox?.role || '')) return;
       const isInJunk = currentMailbox?.role === 'junk';
-      if (selectedEmailIds.size > 0 && client) {
-        const ids = Array.from(selectedEmailIds);
+      if (selectedEmailKeys.size > 0 && client) {
+        const ids = Array.from(selectedEmailKeys);
         try {
           if (isInJunk) {
             await batchUndoSpam(client, ids);
@@ -842,14 +842,14 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
       }
     },
   // eslint-disable-next-line react-hooks/exhaustive-deps
-  }), [activeEmails, selectedEmail, client, selectedMailbox, isMobile, isTablet, selectedEmailIds, mailboxes, isScheduledView]);
+  }), [activeEmails, selectedEmail, client, selectedMailbox, isMobile, isTablet, selectedEmailKeys, mailboxes, isScheduledView]);
 
   // Initialize keyboard shortcuts
   useKeyboardShortcuts({
     enabled: isAuthenticated && !showComposer,
     emails: activeEmails,
     selectedEmailId: selectedEmail?.id,
-    selectionCount: selectedEmailIds.size,
+    selectionCount: selectedEmailKeys.size,
     handlers: keyboardHandlers,
   });
 
@@ -3706,30 +3706,32 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
                   <button
                     type="button"
                     onClick={() => {
-                      if (selectedEmailIds.size > 0) {
-                        if (selectedEmailIds.size === activeEmails.length) {
+                      if (selectedEmailKeys.size > 0) {
+                        if (selectedEmailKeys.size === activeEmails.length) {
                           clearSelection();
                         } else {
                           selectAllEmails();
                         }
                       } else if (activeEmails.length > 0) {
-                        const currentId = selectedEmail?.id;
-                        const target = currentId && activeEmails.some((e) => e.id === currentId)
-                          ? currentId
-                          : activeEmails[0].id;
+                        // The open message when it is in this list, else the
+                        // first row - as an email, so the selection is keyed by
+                        // its owning account and not by a colliding id.
+                        const target = (selectedEmail && activeEmails.some((e) => e.id === selectedEmail.id)
+                          ? activeEmails.find((e) => e.id === selectedEmail.id)
+                          : activeEmails[0])!;
                         toggleEmailSelection(target);
                       }
                     }}
                     disabled={isScheduledView}
                     className={cn(
                       "flex-shrink-0 p-2 rounded-md transition-colors",
-                      selectedEmailIds.size > 0
+                      selectedEmailKeys.size > 0
                         ? "bg-primary/10 text-primary"
                         : "text-muted-foreground hover:text-foreground hover:bg-muted"
                     )}
-                    title={isScheduledView ? t('email_viewer.scheduled_actions_only') : selectedEmailIds.size > 0 ? (selectedEmailIds.size === activeEmails.length ? t('email_list.batch_actions.clear_selection') : t('email_list.batch_actions.select_all')) : t('email_list.batch_actions.select')}
+                    title={isScheduledView ? t('email_viewer.scheduled_actions_only') : selectedEmailKeys.size > 0 ? (selectedEmailKeys.size === activeEmails.length ? t('email_list.batch_actions.clear_selection') : t('email_list.batch_actions.select_all')) : t('email_list.batch_actions.select')}
                   >
-                    {selectedEmailIds.size > 0 ? (
+                    {selectedEmailKeys.size > 0 ? (
                       <CheckSquare className="w-4 h-4" />
                     ) : (
                       <Square className="w-4 h-4" />
diff --git a/hooks/use-email-drag.ts b/hooks/use-email-drag.ts
index fb3a5f071..0bea4c299 100644
--- a/hooks/use-email-drag.ts
+++ b/hooks/use-email-drag.ts
@@ -141,7 +141,7 @@ function getReadyBundle(emails: Email[]): { url: string; name: string } | null {
 }
 
 export function useEmailDrag({ email, sourceMailboxId, threadEmails }: UseEmailDragOptions): UseEmailDragReturn {
-  const { selectedEmailIds, emails } = useEmailStore();
+  const { selectedEmailKeys, emails } = useEmailStore();
   const { startDrag, endDrag, isDragging, draggedEmails } = useDragDropContext();
   const isMobile = useUIStore((state) => state.isMobile);
   const client = useAuthStore((state) => state.client);
@@ -195,10 +195,10 @@ export function useEmailDrag({ email, sourceMailboxId, threadEmails }: UseEmailD
 
   const handlePointerEnter = useCallback(() => {
     if (!dragOutEnabled || !client) return;
-    const isSelected = selectedEmailIds.has(email.id);
-    const isMulti = isSelected && selectedEmailIds.size > 1;
+    const isSelected = selectedEmailKeys.has(email.id);
+    const isMulti = isSelected && selectedEmailKeys.size > 1;
     if (isMulti) {
-      const selected = emails.filter((em) => selectedEmailIds.has(em.id));
+      const selected = emails.filter((em) => selectedEmailKeys.has(em.id));
       // Only worth bundling when at least one selected email has a blobId.
       if (selected.some((em) => em.blobId)) {
         prefetchEmailBundle(client, selected, filenameOptions, bundleOptions);
@@ -206,16 +206,16 @@ export function useEmailDrag({ email, sourceMailboxId, threadEmails }: UseEmailD
     } else {
       prefetchSingle();
     }
-  }, [dragOutEnabled, client, selectedEmailIds, email.id, emails, prefetchSingle, filenameOptions, bundleOptions]);
+  }, [dragOutEnabled, client, selectedEmailKeys, email.id, emails, prefetchSingle, filenameOptions, bundleOptions]);
 
   const handleDragStart = useCallback((e: DragEvent<HTMLDivElement>) => {
     // Determine which emails to drag:
     // - If current email is selected, drag all selected
     // - If threadEmails provided (thread header), drag all thread emails
     // - Otherwise, drag only this email
-    const isSelected = selectedEmailIds.has(email.id);
+    const isSelected = selectedEmailKeys.has(email.id);
     const emailsToDrag = isSelected
-      ? emails.filter(em => selectedEmailIds.has(em.id))
+      ? emails.filter(em => selectedEmailKeys.has(em.id))
       : threadEmails || [email];
 
     e.dataTransfer.effectAllowed = "copyMove";
@@ -284,7 +284,7 @@ export function useEmailDrag({ email, sourceMailboxId, threadEmails }: UseEmailD
     });
 
     startDrag(emailsToDrag, sourceMailboxId);
-  }, [email, selectedEmailIds, emails, sourceMailboxId, startDrag, threadEmails, dragOutEnabled, client, prefetchSingle, filenameOptions, bundleOptions]);
+  }, [email, selectedEmailKeys, emails, sourceMailboxId, startDrag, threadEmails, dragOutEnabled, client, prefetchSingle, filenameOptions, bundleOptions]);
 
   const handleDragEnd = useCallback(() => {
     endDrag();
diff --git a/hooks/use-mailbox-drop.ts b/hooks/use-mailbox-drop.ts
index 4954423ca..2b87b6665 100644
--- a/hooks/use-mailbox-drop.ts
+++ b/hooks/use-mailbox-drop.ts
@@ -65,7 +65,7 @@ interface UseMailboxDropReturn {
 export function useMailboxDrop({ mailbox, onDropComplete, onSuccess, onError }: UseMailboxDropOptions): UseMailboxDropReturn {
   const [isOver, setIsOver] = useState(false);
   const { client } = useAuthStore();
-  const { moveEmailsToMailbox, crossAccountMoveEmails, selectedEmailIds, clearSelection, refreshCurrentMailbox, mailboxes } = useEmailStore();
+  const { moveEmailsToMailbox, crossAccountMoveEmails, selectedEmailKeys, clearSelection, refreshCurrentMailbox, mailboxes } = useEmailStore();
   const { isDragging, sourceMailboxId, draggedEmails, endDrag } = useDragDropContext();
 
   // Determine if this is a valid drop target
@@ -184,7 +184,7 @@ export function useMailboxDrop({ mailbox, onDropComplete, onSuccess, onError }:
       }
 
       // Clear selection if any selected emails were moved
-      if (emailIds.some(id => selectedEmailIds.has(id))) {
+      if (emailIds.some(id => selectedEmailKeys.has(id))) {
         clearSelection();
       }
 
@@ -222,7 +222,7 @@ export function useMailboxDrop({ mailbox, onDropComplete, onSuccess, onError }:
     } finally {
       endDrag();
     }
-  }, [client, mailbox, mailboxes, isValidTarget, moveEmailsToMailbox, crossAccountMoveEmails, draggedEmails, sourceMailboxId, selectedEmailIds, clearSelection, refreshCurrentMailbox, endDrag, onDropComplete, onSuccess, onError]);
+  }, [client, mailbox, mailboxes, isValidTarget, moveEmailsToMailbox, crossAccountMoveEmails, draggedEmails, sourceMailboxId, selectedEmailKeys, clearSelection, refreshCurrentMailbox, endDrag, onDropComplete, onSuccess, onError]);
 
   const valid = isValidTarget();
 
diff --git a/lib/__tests__/account-state-manager.test.ts b/lib/__tests__/account-state-manager.test.ts
index 3ad649036..3231a34e8 100644
--- a/lib/__tests__/account-state-manager.test.ts
+++ b/lib/__tests__/account-state-manager.test.ts
@@ -94,7 +94,7 @@ describe('clearAllStores', () => {
   it('resets the email store to fresh empty collections', () => {
     useEmailStore.setState({
       emails: [makeEmail({ id: 'x' })],
-      selectedEmailIds: new Set(['x']),
+      selectedEmailKeys: new Set(['x']),
       searchQuery: 'q',
       tagCounts: { a: { total: 1, unread: 0 } },
       threadEmailsCache: new Map([['t', []]]),
@@ -105,7 +105,7 @@ describe('clearAllStores', () => {
     const s = useEmailStore.getState();
     expect(s.emails).toEqual([]);
     expect(s.searchQuery).toBe('');
-    expect(s.selectedEmailIds.size).toBe(0);
+    expect(s.selectedEmailKeys.size).toBe(0);
     expect(s.threadEmailsCache.size).toBe(0);
     expect(s.tagCounts).toEqual({});
     expect(s.searchFilters).toEqual(DEFAULT_SEARCH_FILTERS);
diff --git a/lib/account-state-manager.ts b/lib/account-state-manager.ts
index 92fdb092d..d0753a303 100644
--- a/lib/account-state-manager.ts
+++ b/lib/account-state-manager.ts
@@ -117,7 +117,7 @@ export function clearAllStores(): void {
     isPushConnected: false,
     lastPushUpdate: null,
     newEmailNotification: null,
-    selectedEmailIds: new Set<string>(),
+    selectedEmailKeys: new Set<string>(),
     hasMoreEmails: false,
     totalEmails: 0,
     expandedThreadIds: new Set<string>(),
diff --git a/lib/thread-utils.ts b/lib/thread-utils.ts
index a3476c6ec..991da6eb5 100644
--- a/lib/thread-utils.ts
+++ b/lib/thread-utils.ts
@@ -19,6 +19,23 @@ export function threadKeyFor(
   return scope ? `${scope}:${email.threadId}` : email.threadId;
 }
 
+/**
+ * Client-side identity of a single message.
+ *
+ * Email ids are per-account too, so in a merged view two unrelated messages can
+ * share an `id` - `eiaaaabc` exists in every account that got that far. Batch
+ * selection is what makes that dangerous: keyed by the bare id, ticking one row
+ * also ticks its namesake in another account, and delete, move or archive then
+ * act on both. Same scoping as `threadKeyFor`; unstamped emails keep the bare
+ * id, so single-account views are untouched.
+ */
+export function emailKeyFor(
+  email: Pick<Email, "id" | "sourceClientAccountId" | "sourceAccountId">,
+): string {
+  const scope = [email.sourceClientAccountId, email.sourceAccountId].filter(Boolean).join("/");
+  return scope ? `${scope}:${email.id}` : email.id;
+}
+
 /**
  * The JMAP thread id behind a `threadKeyFor` key. JMAP ids never contain ":"
  * (RFC 8620 §1.2 limits them to the URL-safe base64 alphabet), so the last
diff --git a/stores/__tests__/email-archive.test.ts b/stores/__tests__/email-archive.test.ts
index 2522b58a0..c8b3ef67f 100644
--- a/stores/__tests__/email-archive.test.ts
+++ b/stores/__tests__/email-archive.test.ts
@@ -61,7 +61,7 @@ describe('email-store archive thread behavior', () => {
       mailboxes: [inbox, archive],
       selectedMailbox: 'shared-inbox',
       selectedEmail: threadEmailA,
-      selectedEmailIds: new Set(['email-1', 'email-2']),
+      selectedEmailKeys: new Set(['email-1', 'email-2']),
       expandedThreadIds: new Set(['thread-1']),
       threadEmailsCache: new Map([['thread-1', [threadEmailA, threadEmailB]]]),
       error: null,
@@ -82,7 +82,7 @@ describe('email-store archive thread behavior', () => {
     const state = useEmailStore.getState();
     expect(state.emails.map(email => email.id)).toEqual(['email-3']);
     expect(state.selectedEmail?.id).toBe('email-3');
-    expect(Array.from(state.selectedEmailIds)).toEqual([]);
+    expect(Array.from(state.selectedEmailKeys)).toEqual([]);
     expect(state.expandedThreadIds.has('thread-1')).toBe(false);
     expect(state.threadEmailsCache.has('thread-1')).toBe(false);
   });
diff --git a/stores/__tests__/email-selection-cross-account.test.ts b/stores/__tests__/email-selection-cross-account.test.ts
new file mode 100644
index 000000000..cedb7a64f
--- /dev/null
+++ b/stores/__tests__/email-selection-cross-account.test.ts
@@ -0,0 +1,62 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { useEmailStore } from '../email-store';
+import { emailKeyFor } from '@/lib/thread-utils';
+import type { Email } from '@/lib/jmap/types';
+
+/**
+ * Email ids are per-account, so the same id exists in several accounts
+ * ("eiaaaabc" is an ordinary first id). Reported on #1013 by @alyyousuf7:
+ * selection keyed by the bare id ticks both, and a batch action then hits a
+ * message the user never selected.
+ */
+const twin = (account: string, subject: string): Email => ({
+  id: 'eiaaaabc', threadId: 'taaaabc', blobId: `blob-${account}`,
+  mailboxIds: { inbox: true }, keywords: {},
+  from: [{ email: `someone@${account}` }], to: [], subject,
+  receivedAt: '2026-09-19T08:00:00Z', size: 42, preview: '', hasAttachment: false,
+  sourceClientAccountId: account, sourceAccountId: account,
+} as unknown as Email);
+
+const mine = twin('account-a', 'mia');
+const theirs = twin('account-b', 'di un altro account');
+
+beforeEach(() => {
+  useEmailStore.setState({ emails: [mine, theirs], selectedEmailKeys: new Set(), lastSelectedEmailKey: null });
+});
+
+describe('selection across accounts sharing an email id', () => {
+  it('ticks only the row that was clicked', () => {
+    useEmailStore.getState().toggleEmailSelection(mine);
+    const { emails, selectedEmailKeys } = useEmailStore.getState();
+    const affected = emails.filter(e => selectedEmailKeys.has(emailKeyFor(e)));
+    expect(affected).toHaveLength(1);
+    expect(affected[0]!.sourceAccountId).toBe('account-a');
+  });
+
+  it('unticks its namesake independently', () => {
+    const store = useEmailStore.getState();
+    store.toggleEmailSelection(mine);
+    store.toggleEmailSelection(theirs);
+    expect(useEmailStore.getState().selectedEmailKeys.size).toBe(2);
+    store.toggleEmailSelection(theirs);
+    const { selectedEmailKeys } = useEmailStore.getState();
+    expect([...selectedEmailKeys]).toEqual([emailKeyFor(mine)]);
+  });
+
+  it('selects every account copy when the whole list is selected', () => {
+    useEmailStore.getState().selectAllEmails();
+    expect(useEmailStore.getState().selectedEmailKeys.size).toBe(2);
+  });
+
+  it('deletes only the selected account copy', async () => {
+    const client = {
+      batchDeleteEmails: vi.fn(async () => {}),
+      batchMoveToMailbox: vi.fn(async () => {}),
+      getMailboxes: vi.fn(async () => []),
+    } as never;
+    useEmailStore.getState().toggleEmailSelection(theirs);
+    await useEmailStore.getState().batchDelete(client, true);
+    const remaining = useEmailStore.getState().emails;
+    expect(remaining.map(e => e.sourceAccountId)).toEqual(['account-a']);
+  });
+});
diff --git a/stores/__tests__/email-selection.test.ts b/stores/__tests__/email-selection.test.ts
index 6c7411d91..51dffe4d0 100644
--- a/stores/__tests__/email-selection.test.ts
+++ b/stores/__tests__/email-selection.test.ts
@@ -24,29 +24,29 @@ describe('email-store selection', () => {
   beforeEach(() => {
     useEmailStore.setState({
       emails: [makeEmail('a'), makeEmail('b'), makeEmail('c'), makeEmail('d'), makeEmail('e')],
-      selectedEmailIds: new Set(),
-      lastSelectedEmailId: null,
+      selectedEmailKeys: new Set(),
+      lastSelectedEmailKey: null,
       selectedEmail: null,
     });
   });
 
   describe('toggleEmailSelection', () => {
     it('should add email to selection', () => {
-      useEmailStore.getState().toggleEmailSelection('b');
-      expect(useEmailStore.getState().selectedEmailIds.has('b')).toBe(true);
-      expect(useEmailStore.getState().lastSelectedEmailId).toBe('b');
+      useEmailStore.getState().toggleEmailSelection({ id: 'b' });
+      expect(useEmailStore.getState().selectedEmailKeys.has('b')).toBe(true);
+      expect(useEmailStore.getState().lastSelectedEmailKey).toBe('b');
     });
 
     it('should remove email from selection when toggled again', () => {
-      useEmailStore.getState().toggleEmailSelection('b');
-      useEmailStore.getState().toggleEmailSelection('b');
-      expect(useEmailStore.getState().selectedEmailIds.has('b')).toBe(false);
+      useEmailStore.getState().toggleEmailSelection({ id: 'b' });
+      useEmailStore.getState().toggleEmailSelection({ id: 'b' });
+      expect(useEmailStore.getState().selectedEmailKeys.has('b')).toBe(false);
     });
 
     it('should support selecting multiple emails', () => {
-      useEmailStore.getState().toggleEmailSelection('a');
-      useEmailStore.getState().toggleEmailSelection('c');
-      const ids = useEmailStore.getState().selectedEmailIds;
+      useEmailStore.getState().toggleEmailSelection({ id: 'a' });
+      useEmailStore.getState().toggleEmailSelection({ id: 'c' });
+      const ids = useEmailStore.getState().selectedEmailKeys;
       expect(ids.has('a')).toBe(true);
       expect(ids.has('c')).toBe(true);
       expect(ids.size).toBe(2);
@@ -55,9 +55,9 @@ describe('email-store selection', () => {
 
   describe('selectRangeEmails', () => {
     it('should select range from last selected to target (forward)', () => {
-      useEmailStore.getState().toggleEmailSelection('b'); // anchor at index 1
-      useEmailStore.getState().selectRangeEmails('d'); // target at index 3
-      const ids = useEmailStore.getState().selectedEmailIds;
+      useEmailStore.getState().toggleEmailSelection({ id: 'b' }); // anchor at index 1
+      useEmailStore.getState().selectRangeEmails({ id: 'd' }); // target at index 3
+      const ids = useEmailStore.getState().selectedEmailKeys;
       expect(ids.has('b')).toBe(true);
       expect(ids.has('c')).toBe(true);
       expect(ids.has('d')).toBe(true);
@@ -65,9 +65,9 @@ describe('email-store selection', () => {
     });
 
     it('should select range backward', () => {
-      useEmailStore.getState().toggleEmailSelection('d'); // anchor at index 3
-      useEmailStore.getState().selectRangeEmails('b'); // target at index 1
-      const ids = useEmailStore.getState().selectedEmailIds;
+      useEmailStore.getState().toggleEmailSelection({ id: 'd' }); // anchor at index 3
+      useEmailStore.getState().selectRangeEmails({ id: 'b' }); // target at index 1
+      const ids = useEmailStore.getState().selectedEmailKeys;
       expect(ids.has('b')).toBe(true);
       expect(ids.has('c')).toBe(true);
       expect(ids.has('d')).toBe(true);
@@ -75,8 +75,8 @@ describe('email-store selection', () => {
     });
 
     it('should use first email as anchor when no previous selection', () => {
-      useEmailStore.getState().selectRangeEmails('c'); // no anchor → uses first email 'a'
-      const ids = useEmailStore.getState().selectedEmailIds;
+      useEmailStore.getState().selectRangeEmails({ id: 'c' }); // no anchor → uses first email 'a'
+      const ids = useEmailStore.getState().selectedEmailKeys;
       expect(ids.has('a')).toBe(true);
       expect(ids.has('b')).toBe(true);
       expect(ids.has('c')).toBe(true);
@@ -84,10 +84,10 @@ describe('email-store selection', () => {
     });
 
     it('should add to existing selection', () => {
-      useEmailStore.getState().toggleEmailSelection('a');
-      useEmailStore.getState().toggleEmailSelection('b'); // anchor now at 'b'
-      useEmailStore.getState().selectRangeEmails('d');
-      const ids = useEmailStore.getState().selectedEmailIds;
+      useEmailStore.getState().toggleEmailSelection({ id: 'a' });
+      useEmailStore.getState().toggleEmailSelection({ id: 'b' }); // anchor now at 'b'
+      useEmailStore.getState().selectRangeEmails({ id: 'd' });
+      const ids = useEmailStore.getState().selectedEmailKeys;
       // 'a' still selected, plus b-d range
       expect(ids.has('a')).toBe(true);
       expect(ids.has('b')).toBe(true);
@@ -97,9 +97,9 @@ describe('email-store selection', () => {
     });
 
     it('should handle single-item range', () => {
-      useEmailStore.getState().toggleEmailSelection('c');
-      useEmailStore.getState().selectRangeEmails('c');
-      const ids = useEmailStore.getState().selectedEmailIds;
+      useEmailStore.getState().toggleEmailSelection({ id: 'c' });
+      useEmailStore.getState().selectRangeEmails({ id: 'c' });
+      const ids = useEmailStore.getState().selectedEmailKeys;
       expect(ids.has('c')).toBe(true);
       expect(ids.size).toBe(1);
     });
@@ -108,17 +108,17 @@ describe('email-store selection', () => {
   describe('selectAllEmails', () => {
     it('should select all emails', () => {
       useEmailStore.getState().selectAllEmails();
-      expect(useEmailStore.getState().selectedEmailIds.size).toBe(5);
+      expect(useEmailStore.getState().selectedEmailKeys.size).toBe(5);
     });
   });
 
   describe('clearSelection', () => {
     it('should clear all selections and reset anchor', () => {
-      useEmailStore.getState().toggleEmailSelection('a');
-      useEmailStore.getState().toggleEmailSelection('b');
+      useEmailStore.getState().toggleEmailSelection({ id: 'a' });
+      useEmailStore.getState().toggleEmailSelection({ id: 'b' });
       useEmailStore.getState().clearSelection();
-      expect(useEmailStore.getState().selectedEmailIds.size).toBe(0);
-      expect(useEmailStore.getState().lastSelectedEmailId).toBeNull();
+      expect(useEmailStore.getState().selectedEmailKeys.size).toBe(0);
+      expect(useEmailStore.getState().lastSelectedEmailKey).toBeNull();
     });
   });
 });
diff --git a/stores/__tests__/email-store-archive-missing.test.ts b/stores/__tests__/email-store-archive-missing.test.ts
index cce2d45f5..983cff55b 100644
--- a/stores/__tests__/email-store-archive-missing.test.ts
+++ b/stores/__tests__/email-store-archive-missing.test.ts
@@ -74,7 +74,7 @@ describe('batchArchive without an archive mailbox (#578)', () => {
       ],
       accountMailboxes: {},
       emails: [makeEmail({ id: 'e1', mailboxIds: { 'a-inbox': true } })],
-      selectedEmailIds: new Set(['e1']),
+      selectedEmailKeys: new Set(['e1']),
     });
   });
 
@@ -86,6 +86,6 @@ describe('batchArchive without an archive mailbox (#578)', () => {
     expect(useEmailStore.getState().error).toMatch(/archive mailbox not found/i);
     expect(client.batchArchiveEmails).not.toHaveBeenCalled();
     // Nothing was archived, so the selection must survive.
-    expect(useEmailStore.getState().selectedEmailIds.has('e1')).toBe(true);
+    expect(useEmailStore.getState().selectedEmailKeys.has('e1')).toBe(true);
   });
 });
diff --git a/stores/__tests__/email-store-multi-account.test.ts b/stores/__tests__/email-store-multi-account.test.ts
index 02a5cacbb..280be7514 100644
--- a/stores/__tests__/email-store-multi-account.test.ts
+++ b/stores/__tests__/email-store-multi-account.test.ts
@@ -36,7 +36,7 @@ describe('useEmailStore multi-account state', () => {
       viewingAccountId: null,
       selectedMailbox: '',
       selectedEmail: null,
-      selectedEmailIds: new Set(),
+      selectedEmailKeys: new Set(),
       selectedKeyword: null,
       expandedThreadIds: new Set(),
       threadEmailsCache: new Map(),
@@ -89,7 +89,7 @@ describe('useEmailStore multi-account state', () => {
   it('selectAccountMailbox sets viewing and selected together, and clears email selection state', () => {
     useEmailStore.setState({
       selectedEmail: { id: 'e1' } as unknown as ReturnType<typeof useEmailStore.getState>['selectedEmail'],
-      selectedEmailIds: new Set(['e1', 'e2']),
+      selectedEmailKeys: new Set(['e1', 'e2']),
       selectedKeyword: 'work',
       expandedThreadIds: new Set(['thread-1']),
     });
@@ -100,7 +100,7 @@ describe('useEmailStore multi-account state', () => {
     expect(state.viewingAccountId).toBe('account-b');
     expect(state.selectedMailbox).toBe('b-inbox');
     expect(state.selectedEmail).toBeNull();
-    expect(state.selectedEmailIds.size).toBe(0);
+    expect(state.selectedEmailKeys.size).toBe(0);
     expect(state.selectedKeyword).toBeNull();
     expect(state.expandedThreadIds.size).toBe(0);
   });
diff --git a/stores/__tests__/email-store-retained-in-view.test.ts b/stores/__tests__/email-store-retained-in-view.test.ts
index 43e2df61f..cdf3f1ba7 100644
--- a/stores/__tests__/email-store-retained-in-view.test.ts
+++ b/stores/__tests__/email-store-retained-in-view.test.ts
@@ -78,7 +78,7 @@ function seedView(id: typeof CROSS_UNREAD | typeof CROSS_STARRED, view: 'unread'
     mailboxes: [makeMailbox()],
     accountMailboxes: { 'account-a': [makeMailbox()] },
     processingReadStatus: new Set(),
-    selectedEmailIds: new Set(),
+    selectedEmailKeys: new Set(),
     retainedInViewIds: new Set(),
     emails,
     totalEmails: emails.length,
@@ -194,7 +194,7 @@ describe('retained-in-view: scope', () => {
       isUnifiedView: true, unifiedRole: null, crossView: 'all', selectedMailbox: '__cross_all__',
       selectedKeyword: null, searchQuery: '', mailboxes: [makeMailbox()],
       accountMailboxes: { 'account-a': [makeMailbox()] },
-      processingReadStatus: new Set(), selectedEmailIds: new Set(), retainedInViewIds: new Set(),
+      processingReadStatus: new Set(), selectedEmailKeys: new Set(), retainedInViewIds: new Set(),
       emails: [a], totalEmails: 1,
     });
 
diff --git a/stores/__tests__/email-store-shared-folder-actions.test.ts b/stores/__tests__/email-store-shared-folder-actions.test.ts
index e778c807c..dd3e55830 100644
--- a/stores/__tests__/email-store-shared-folder-actions.test.ts
+++ b/stores/__tests__/email-store-shared-folder-actions.test.ts
@@ -118,7 +118,7 @@ describe('non-unified shared-folder batch action routing', () => {
         makeEmail({ id: 'e1', keywords: {}, mailboxIds: { 'owner-x:x-inbox': true } }),
         makeEmail({ id: 'e2', keywords: {}, mailboxIds: { 'owner-x:x-inbox': true } }),
       ],
-      selectedEmailIds: new Set(['e1', 'e2']),
+      selectedEmailKeys: new Set(['e1', 'e2']),
     });
   });
 
@@ -185,7 +185,7 @@ describe('non-unified shared-folder batch action routing', () => {
         makeEmail({ id: 'o1', keywords: {}, mailboxIds: { 'a-inbox': true } }),
         makeEmail({ id: 'o2', keywords: {}, mailboxIds: { 'a-inbox': true } }),
       ],
-      selectedEmailIds: new Set(['o1', 'o2']),
+      selectedEmailKeys: new Set(['o1', 'o2']),
     });
 
     await useEmailStore.getState().batchDelete(activeClient, false);
diff --git a/stores/__tests__/email-store-shared-folder-keywords.test.ts b/stores/__tests__/email-store-shared-folder-keywords.test.ts
index 97659d646..ff51348aa 100644
--- a/stores/__tests__/email-store-shared-folder-keywords.test.ts
+++ b/stores/__tests__/email-store-shared-folder-keywords.test.ts
@@ -101,7 +101,7 @@ describe('non-unified shared-folder keyword routing', () => {
       accountMailboxes: {},
       selectedEmail: null,
       emails: [makeEmail({ id: 'e1', keywords: {}, mailboxIds: { 'owner-x:x-inbox': true } })],
-      selectedEmailIds: new Set<string>(),
+      selectedEmailKeys: new Set<string>(),
     } as never);
   });
 
diff --git a/stores/__tests__/email-store-tag-counts.test.ts b/stores/__tests__/email-store-tag-counts.test.ts
index b99ea9fdf..fd3cd50ea 100644
--- a/stores/__tests__/email-store-tag-counts.test.ts
+++ b/stores/__tests__/email-store-tag-counts.test.ts
@@ -86,7 +86,7 @@ describe('email-store tag counts stay in step with read state', () => {
       accountMailboxes: {},
       emails: [],
       selectedEmail: null,
-      selectedEmailIds: new Set(),
+      selectedEmailKeys: new Set(),
       processingReadStatus: new Set(),
       threadEmailsCache: new Map(),
       tagCounts: {
@@ -187,7 +187,7 @@ describe('email-store tag counts stay in step with read state', () => {
           // Untagged: must not contribute a delta.
           makeEmail({ id: 'e4', keywords: {} }),
         ],
-        selectedEmailIds: new Set(['e1', 'e2', 'e3', 'e4']),
+        selectedEmailKeys: new Set(['e1', 'e2', 'e3', 'e4']),
       } as never);
 
       await useEmailStore.getState().batchMarkAsRead(client, true);
diff --git a/stores/__tests__/email-store-tag-view-accounts.test.ts b/stores/__tests__/email-store-tag-view-accounts.test.ts
index c1a896315..c4fed1fdf 100644
--- a/stores/__tests__/email-store-tag-view-accounts.test.ts
+++ b/stores/__tests__/email-store-tag-view-accounts.test.ts
@@ -1,5 +1,6 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 import { useEmailStore } from '../email-store';
+import { emailKeyFor } from '@/lib/thread-utils';
 import { useSettingsStore } from '../settings-store';
 import { useAuthStore } from '../auth-store';
 import { useMessageListTabsStore } from '../message-list-tabs-store';
@@ -137,7 +138,10 @@ describe('tag view across the own and group accounts (#1038)', () => {
     useEmailStore.setState({ selectedMailbox: groupInbox.id });
     useEmailStore.getState().selectKeyword(label);
     await useEmailStore.getState().fetchEmails(client);
-    useEmailStore.setState({ selectedEmailIds: new Set(['own-1', 'grp-1']) });
+    // Keyed by owning account: in this very view 'own-1' and 'grp-1' could be
+    // the same bare id in two accounts.
+    const picked = useEmailStore.getState().emails.filter(e => ['own-1', 'grp-1'].includes(e.id));
+    useEmailStore.setState({ selectedEmailKeys: new Set(picked.map(emailKeyFor)) });
 
     await useEmailStore.getState().batchMarkAsRead(client, true);
 
diff --git a/stores/__tests__/email-store-unified-actions.test.ts b/stores/__tests__/email-store-unified-actions.test.ts
index 68a782b8f..fb50d14fe 100644
--- a/stores/__tests__/email-store-unified-actions.test.ts
+++ b/stores/__tests__/email-store-unified-actions.test.ts
@@ -1,5 +1,6 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 import { useEmailStore } from '../email-store';
+import { emailKeyFor } from '@/lib/thread-utils';
 import { useAuthStore } from '../auth-store';
 import type { Email, Mailbox } from '@/lib/jmap/types';
 import type { IJMAPClient } from '@/lib/jmap/client-interface';
@@ -98,7 +99,7 @@ describe('unified-view single-email action routing (#281)', () => {
       },
       processingReadStatus: new Set(),
       selectedEmail: null,
-      selectedEmailIds: new Set(),
+      selectedEmailKeys: new Set(),
       unifiedScope: [],
       unifiedCounts: [],
       crossUnreadCount: 0,
@@ -164,7 +165,10 @@ describe('unified-view single-email action routing (#281)', () => {
         makeEmail({ id: 'a1', sourceClientAccountId: 'account-a', sourceAccountId: 'account-a', keywords: {}, mailboxIds: { inbox: true } }),
         makeEmail({ id: 'b1', sourceClientAccountId: 'account-b', sourceAccountId: 'account-b', keywords: {}, mailboxIds: { inbox: true } }),
       ],
-      selectedEmailIds: new Set(['a1', 'b1']),
+      selectedEmailKeys: new Set([
+        emailKeyFor({ id: 'a1', sourceClientAccountId: 'account-a', sourceAccountId: 'account-a' }),
+        emailKeyFor({ id: 'b1', sourceClientAccountId: 'account-b', sourceAccountId: 'account-b' }),
+      ]),
     });
 
     await useEmailStore.getState().batchMarkAsRead(activeClient, true);
@@ -209,7 +213,9 @@ describe('unified-view single-email action routing (#281)', () => {
           mailboxIds: { 'x-inbox': true }, // BARE owner id (not namespaced)
         }),
       ],
-      selectedEmailIds: new Set(['email-shared']),
+      selectedEmailKeys: new Set([
+        emailKeyFor({ id: 'email-shared', sourceClientAccountId: 'account-a', sourceAccountId: 'owner-x' }),
+      ]),
     });
 
     await useEmailStore.getState().batchDelete(activeClient, true);
@@ -255,7 +261,9 @@ describe('unified-view single-email action routing (#281)', () => {
           mailboxIds: { 'x-inbox': true }, // BARE owner id (not namespaced)
         }),
       ],
-      selectedEmailIds: new Set(['email-shared']),
+      selectedEmailKeys: new Set([
+        emailKeyFor({ id: 'email-shared', sourceClientAccountId: 'account-a', sourceAccountId: 'owner-x' }),
+      ]),
     });
 
     // Seed the badges from the scope (also stores unifiedScope).
diff --git a/stores/email-store.ts b/stores/email-store.ts
index c10ac3a1a..33d25acf5 100644
--- a/stores/email-store.ts
+++ b/stores/email-store.ts
@@ -8,7 +8,7 @@ import type { SortLevel } from "@/lib/message-list-order";
 import { SearchFilters, DEFAULT_SEARCH_FILTERS, buildJMAPFilter, isFilterEmpty } from "@/lib/jmap/search-utils";
 import { emailHooks } from "@/lib/plugin-hooks";
 import { resolveThreadRoute } from "@/lib/thread-routing";
-import { threadKeyFor, threadIdFromKey } from "@/lib/thread-utils";
+import { emailKeyFor, threadKeyFor, threadIdFromKey } from "@/lib/thread-utils";
 import type { ExternalSearchResult } from "@/lib/plugin-types";
 import { fetchUnifiedEmails, fetchUnifiedMailboxCounts, searchUnifiedEmails, advancedSearchUnifiedEmails, fetchCrossViewEmails, searchCrossViewEmails, advancedSearchCrossViewEmails, fetchTagEmails, getCrossUnreadTotal, type UnifiedAccountClient, type UnifiedMailboxCounts } from "@/lib/unified-mailbox";
 import { useAuthStore } from "@/stores/auth-store";
@@ -41,6 +41,19 @@ type PendingUndoSend = {
   submissionAccountId?: string;
 };
 
+/** Drop the matching emails from a key-based selection. */
+function dropFromSelection(
+  state: { emails: Email[]; selectedEmailKeys: Set<string> },
+  matches: (email: Email) => boolean,
+): Set<string> {
+  const next = new Set(state.selectedEmailKeys);
+  for (const email of state.emails) if (matches(email)) next.delete(emailKeyFor(email));
+  return next;
+}
+
+/** Enough of an email to key a selection by its owning account. */
+type SelectableEmail = Pick<Email, 'id' | 'sourceClientAccountId' | 'sourceAccountId'>;
+
 interface EmailStore {
   emails: Email[];
   mailboxes: Mailbox[];
@@ -68,7 +81,7 @@ interface EmailStore {
   searchQuery: string;
   quota: { used: number; total: number } | null;
   processingReadStatus: Set<string>; // Track emails being marked as read/unread
-  selectedEmailIds: Set<string>; // Track selected emails for batch operations
+  selectedEmailKeys: Set<string>; // Track selected emails for batch operations
   // Emails the user just read (unread view) or unstarred (starred view) that
   // should stay visible in that self-filtering cross view until it is re-opened,
   // instead of vanishing on the next push refresh. Cleared on navigation.
@@ -189,9 +202,10 @@ interface EmailStore {
   setQuota: (quota: { used: number; total: number } | null) => void;
   selectKeyword: (keyword: string | null) => void;
   fetchTagCounts: (client: IJMAPClient) => Promise<void>;
-  toggleEmailSelection: (emailId: string) => void;
-  selectRangeEmails: (targetEmailId: string) => void;
-  lastSelectedEmailId: string | null;
+  /** Take the email, not its id: the id alone collides across accounts. */
+  toggleEmailSelection: (email: SelectableEmail) => void;
+  selectRangeEmails: (target: SelectableEmail) => void;
+  lastSelectedEmailKey: string | null;
   selectAllEmails: () => void;
   clearSelection: () => void;
 
@@ -1356,9 +1370,9 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
   searchQuery: "",
   quota: null,
   processingReadStatus: new Set(),
-  selectedEmailIds: new Set(),
+  selectedEmailKeys: new Set(),
   retainedInViewIds: new Set(),
-  lastSelectedEmailId: null,
+  lastSelectedEmailKey: null,
   hasMoreEmails: false,
   totalEmails: 0,
   listOrder: [],
@@ -1422,7 +1436,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
     selectedMailbox: mailboxId,
     isLoadingMore: false,
     selectedEmail: null,
-    selectedEmailIds: new Set(),
+    selectedEmailKeys: new Set(),
     selectedKeyword: null,
     expandedThreadIds: new Set(),
     threadEmailsCache: new Map(),
@@ -1455,7 +1469,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
   },
   selectEmail: (email) => {
     const prev = get().selectedEmail;
-    set({ selectedEmail: email, lastSelectedEmailId: email?.id ?? get().lastSelectedEmailId });
+    set({ selectedEmail: email, lastSelectedEmailKey: email?.id ?? get().lastSelectedEmailKey });
     if (prev && (!email || email.id !== prev.id)) {
       emailHooks.onEmailClose.emitSync(prev);
     }
@@ -1467,7 +1481,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
     selectedKeyword: keyword,
     isLoadingMore: false,
     selectedEmail: null,
-    selectedEmailIds: new Set(),
+    selectedEmailKeys: new Set(),
     expandedThreadIds: new Set(),
     threadEmailsCache: new Map(),
     threadEmailCounts: new Map(),
@@ -1504,7 +1518,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
     selectedMailbox: mailboxId,
     isLoadingMore: false,
     selectedEmail: null,
-    selectedEmailIds: new Set(),
+    selectedEmailKeys: new Set(),
     selectedKeyword: null,
     expandedThreadIds: new Set(),
     threadEmailsCache: new Map(),
@@ -1517,41 +1531,42 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
   setSearchQuery: (query) => set({ searchQuery: query }),
   setQuota: (quota) => set({ quota }),
 
-  toggleEmailSelection: (emailId) => {
-    const { selectedEmailIds } = get();
-    const newSelection = new Set(selectedEmailIds);
-    if (newSelection.has(emailId)) {
-      newSelection.delete(emailId);
+  toggleEmailSelection: (email) => {
+    const key = emailKeyFor(email);
+    const { selectedEmailKeys } = get();
+    const newSelection = new Set(selectedEmailKeys);
+    if (newSelection.has(key)) {
+      newSelection.delete(key);
     } else {
-      newSelection.add(emailId);
+      newSelection.add(key);
     }
-    set({ selectedEmailIds: newSelection, lastSelectedEmailId: emailId });
+    set({ selectedEmailKeys: newSelection, lastSelectedEmailKey: key });
   },
 
-  selectRangeEmails: (targetEmailId) => {
-    const { emails, lastSelectedEmailId, selectedEmailIds } = get();
-    const anchorId = lastSelectedEmailId || emails[0]?.id;
-    if (!anchorId) return;
-    const anchorIndex = emails.findIndex(e => e.id === anchorId);
-    const targetIndex = emails.findIndex(e => e.id === targetEmailId);
+  selectRangeEmails: (target) => {
+    const { emails, lastSelectedEmailKey, selectedEmailKeys } = get();
+    const anchorKey = lastSelectedEmailKey || (emails[0] && emailKeyFor(emails[0]));
+    if (!anchorKey) return;
+    const anchorIndex = emails.findIndex(e => emailKeyFor(e) === anchorKey);
+    const targetKey = emailKeyFor(target);
+    const targetIndex = emails.findIndex(e => emailKeyFor(e) === targetKey);
     if (anchorIndex === -1 || targetIndex === -1) return;
     const start = Math.min(anchorIndex, targetIndex);
     const end = Math.max(anchorIndex, targetIndex);
-    const newSelection = new Set(selectedEmailIds);
+    const newSelection = new Set(selectedEmailKeys);
     for (let i = start; i <= end; i++) {
-      newSelection.add(emails[i].id);
+      newSelection.add(emailKeyFor(emails[i]));
     }
-    set({ selectedEmailIds: newSelection });
+    set({ selectedEmailKeys: newSelection });
   },
 
   selectAllEmails: () => {
     const { emails } = get();
-    const allIds = new Set(emails.map(e => e.id));
-    set({ selectedEmailIds: allIds });
+    set({ selectedEmailKeys: new Set(emails.map(emailKeyFor)) });
   },
 
   clearSelection: () => {
-    set({ selectedEmailIds: new Set(), lastSelectedEmailId: null });
+    set({ selectedEmailKeys: new Set(), lastSelectedEmailKey: null });
   },
 
   // JMAP operations
@@ -2508,9 +2523,10 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
         return {
           emails: state.emails.filter(e => !idSet.has(e.id)),
           selectedEmail: state.selectedEmail && idSet.has(state.selectedEmail.id) ? null : state.selectedEmail,
-          selectedEmailIds: (() => {
-            const next = new Set(state.selectedEmailIds);
-            for (const id of idSet) next.delete(id);
+          selectedEmailKeys: (() => {
+            const next = new Set(state.selectedEmailKeys);
+            // Keys, not ids: drop exactly the emails leaving the list.
+            for (const e of state.emails) if (idSet.has(e.id)) next.delete(emailKeyFor(e));
             return next;
           })(),
           ...patch,
@@ -2601,9 +2617,9 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
           state.selectedEmail && movedSet.has(state.selectedEmail.id)
             ? null
             : state.selectedEmail,
-        selectedEmailIds: (() => {
-          const next = new Set(state.selectedEmailIds);
-          for (const id of movedIds) next.delete(id);
+        selectedEmailKeys: (() => {
+          const next = new Set(state.selectedEmailKeys);
+          for (const e of state.emails) if (movedSet.has(e.id)) next.delete(emailKeyFor(e));
           return next;
         })(),
         isLoading: false,
@@ -2673,8 +2689,11 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
       const removedEmailIds = new Set(threadEmailIds);
       set((currentState) => {
         const nextSelectedEmail = getNextSelectedEmailAfterRemoval(currentState, removedEmailIds);
+        const removedKeys = new Set(
+          currentState.emails.filter(e => removedEmailIds.has(e.id)).map(emailKeyFor)
+        );
         const nextSelectedEmailIds = new Set(
-          Array.from(currentState.selectedEmailIds).filter(id => !removedEmailIds.has(id))
+          Array.from(currentState.selectedEmailKeys).filter(key => !removedKeys.has(key))
         );
         const nextExpandedThreadIds = new Set(currentState.expandedThreadIds);
         nextExpandedThreadIds.delete(threadKeyFor(email));
@@ -2684,7 +2703,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
         return {
           emails: currentState.emails.filter(currentEmail => !removedEmailIds.has(currentEmail.id)),
           selectedEmail: nextSelectedEmail,
-          selectedEmailIds: nextSelectedEmailIds,
+          selectedEmailKeys: nextSelectedEmailIds,
           expandedThreadIds: nextExpandedThreadIds,
           threadEmailsCache: nextThreadEmailsCache,
         };
@@ -3002,21 +3021,24 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
 
   // Batch operations
   batchMarkAsRead: async (client, read) => {
-    const { selectedEmailIds, emails } = get();
-    if (selectedEmailIds.size === 0) return;
+    const { selectedEmailKeys, emails } = get();
+    if (selectedEmailKeys.size === 0) return;
 
     set({ isLoading: true, error: null });
     try {
-      const emailIdsArray = Array.from(selectedEmailIds);
+      // The selection is keyed by owning account; JMAP takes the bare ids of
+      // exactly those emails, never the keys and never a lookup by id (which
+      // is what let a namesake in another account ride along).
+      const selectedEmails = emails.filter(e => selectedEmailKeys.has(emailKeyFor(e)));
+      const emailIdsArray = selectedEmails.map(e => e.id);
 
       if (isAggregateListView()) {
         // Group by owning JMAP account; dispatch through the reaching login client.
         const bySource = new Map<string, { clientAccountId?: string; ids: string[] }>();
-        for (const emailId of emailIdsArray) {
-          const email = emails.find(e => e.id === emailId);
-          const key = email?.sourceAccountId || '__default__';
-          if (!bySource.has(key)) bySource.set(key, { clientAccountId: email?.sourceClientAccountId, ids: [] });
-          bySource.get(key)!.ids.push(emailId);
+        for (const email of selectedEmails) {
+          const key = email.sourceAccountId || '__default__';
+          if (!bySource.has(key)) bySource.set(key, { clientAccountId: email.sourceClientAccountId, ids: [] });
+          bySource.get(key)!.ids.push(email.id);
         }
 
         const promises = Array.from(bySource.entries()).map(async ([sourceAccountId, { clientAccountId, ids }]) => {
@@ -3036,13 +3058,13 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
 
       // Update local state
       const updatedEmails = emails.map(email =>
-        selectedEmailIds.has(email.id)
+        selectedEmailKeys.has(emailKeyFor(email))
           ? { ...email, keywords: { ...email.keywords, $seen: read } }
           : email
       );
 
       // Update mailbox counters per the email's own account list (#281).
-      const affectedEmails = emails.filter(e => selectedEmailIds.has(e.id));
+      const affectedEmails = emails.filter(e => selectedEmailKeys.has(emailKeyFor(e)));
       const mailboxPatch = applyBatchMailboxCounterUpdate(get(), affectedEmails, (mailbox, group) => {
         let deltaUnread = 0;
         for (const email of group as Email[]) {
@@ -3081,7 +3103,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
         ...mailboxPatch,
         tagCounts,
         retainedInViewIds,
-        selectedEmailIds: new Set(),
+        selectedEmailKeys: new Set(),
         isLoading: false
       });
     } catch (error) {
@@ -3093,13 +3115,17 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
   },
 
   batchDelete: async (client, permanent = false) => {
-    const { selectedEmailIds, emails, selectedMailbox } = get();
+    const { selectedEmailKeys, emails, selectedMailbox } = get();
     const mailboxes = resolveActionMailboxes();
-    if (selectedEmailIds.size === 0) return;
+    if (selectedEmailKeys.size === 0) return;
 
     set({ isLoading: true, error: null });
     try {
-      const emailIdsArray = Array.from(selectedEmailIds);
+      // The selection is keyed by owning account; JMAP takes the bare ids of
+      // exactly those emails, never the keys and never a lookup by id (which
+      // is what let a namesake in another account ride along).
+      const selectedEmails = emails.filter(e => selectedEmailKeys.has(emailKeyFor(e)));
+      const emailIdsArray = selectedEmails.map(e => e.id);
 
       // Determine if the current folder forces permanent deletion.
       const currentMailbox = mailboxes.find(m => m.id === selectedMailbox);
@@ -3183,7 +3209,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
           set({
             emails: remainingEmails,
             ...mailboxPatch,
-            selectedEmailIds: new Set(),
+            selectedEmailKeys: new Set(),
             selectedEmail: null,
             isLoading: false,
             error: 'Some emails could not be moved: trash folder missing for one or more accounts',
@@ -3193,16 +3219,16 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
       }
 
       // Remove deleted emails from local state
-      const remainingEmails = emails.filter(e => !selectedEmailIds.has(e.id));
+      const remainingEmails = emails.filter(e => !selectedEmailKeys.has(emailKeyFor(e)));
 
       // Update mailbox counters per the email's own account list (#281).
-      const deletedEmails = emails.filter(e => selectedEmailIds.has(e.id));
+      const deletedEmails = emails.filter(e => selectedEmailKeys.has(emailKeyFor(e)));
       const mailboxPatch = applyBatchMailboxCounterUpdate(get(), deletedEmails, applyDeleteCounters);
 
       set({
         emails: remainingEmails,
         ...mailboxPatch,
-        selectedEmailIds: new Set(),
+        selectedEmailKeys: new Set(),
         selectedEmail: null,
         isLoading: false
       });
@@ -3215,23 +3241,26 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
   },
 
   batchMoveToMailbox: async (client, toMailboxId) => {
-    const { selectedEmailIds, emails } = get();
-    if (selectedEmailIds.size === 0) return;
+    const { selectedEmailKeys, emails } = get();
+    if (selectedEmailKeys.size === 0) return;
 
     set({ isLoading: true, error: null });
     try {
-      const emailIdsArray = Array.from(selectedEmailIds);
+      // The selection is keyed by owning account; JMAP takes the bare ids of
+      // exactly those emails, never the keys and never a lookup by id (which
+      // is what let a namesake in another account ride along).
+      const selectedEmails = emails.filter(e => selectedEmailKeys.has(emailKeyFor(e)));
+      const emailIdsArray = selectedEmails.map(e => e.id);
 
       if (isAggregateListView()) {
         // Group by owning JMAP account; dispatch through the reaching login client.
         const destMailbox = resolveActionMailboxes().find(mb => mb.id === toMailboxId);
         const jmapDestId = destMailbox?.originalId || toMailboxId;
         const bySource = new Map<string, { clientAccountId?: string; ids: string[] }>();
-        for (const emailId of emailIdsArray) {
-          const email = emails.find(e => e.id === emailId);
-          const key = email?.sourceAccountId || '__default__';
-          if (!bySource.has(key)) bySource.set(key, { clientAccountId: email?.sourceClientAccountId, ids: [] });
-          bySource.get(key)!.ids.push(emailId);
+        for (const email of selectedEmails) {
+          const key = email.sourceAccountId || '__default__';
+          if (!bySource.has(key)) bySource.set(key, { clientAccountId: email.sourceClientAccountId, ids: [] });
+          bySource.get(key)!.ids.push(email.id);
         }
 
         const promises = Array.from(bySource.entries()).map(async ([sourceAccountId, { clientAccountId, ids }]) => {
@@ -3254,11 +3283,11 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
       }
 
       // Update local state - remove from current view since they moved
-      const remainingEmails = emails.filter(e => !selectedEmailIds.has(e.id));
+      const remainingEmails = emails.filter(e => !selectedEmailKeys.has(emailKeyFor(e)));
 
       set({
         emails: remainingEmails,
-        selectedEmailIds: new Set(),
+        selectedEmailKeys: new Set(),
         isLoading: false
       });
 
@@ -3275,9 +3304,9 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
   },
 
   batchArchive: async (client) => {
-    const { selectedEmailIds, emails } = get();
+    const { selectedEmailKeys, emails } = get();
     const mailboxes = resolveActionMailboxes();
-    if (selectedEmailIds.size === 0) return;
+    if (selectedEmailKeys.size === 0) return;
 
     // Scope the archive folder to the viewed shared/group account (if any) so the
     // move lands on the owner account, not the user's own archive (which appears
@@ -3292,7 +3321,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
     const mode = useSettingsStore.getState().archiveMode;
     const archiveId = archiveMailbox.originalId || archiveMailbox.id;
 
-    const selected = emails.filter(e => selectedEmailIds.has(e.id));
+    const selected = emails.filter(e => selectedEmailKeys.has(emailKeyFor(e)));
     if (selected.length === 0) return;
 
     set({ isLoading: true, error: null });
@@ -3305,8 +3334,8 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
         archiveMailbox.accountId,
       );
 
-      const remaining = emails.filter(e => !selectedEmailIds.has(e.id));
-      set({ emails: remaining, selectedEmailIds: new Set(), isLoading: false });
+      const remaining = emails.filter(e => !selectedEmailKeys.has(emailKeyFor(e)));
+      set({ emails: remaining, selectedEmailKeys: new Set(), isLoading: false });
 
       // Refresh the active or viewed account's mailbox cache after the
       // archive (a year/month archive can create new sub-folders).
@@ -3546,7 +3575,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
         return {
           emails: state.emails.filter(e => !emailIds.includes(e.id)),
           selectedEmail: emailIds.includes(state.selectedEmail?.id || '') ? null : state.selectedEmail,
-          selectedEmailIds: new Set(),
+          selectedEmailKeys: new Set(),
           ...patch,
         };
       });
@@ -3610,7 +3639,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
         return {
           emails: state.emails.filter(e => !emailIds.includes(e.id)),
           selectedEmail: emailIds.includes(state.selectedEmail?.id || '') ? null : state.selectedEmail,
-          selectedEmailIds: new Set(),
+          selectedEmailKeys: new Set(),
           ...patch,
         };
       });
@@ -4703,7 +4732,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
       scheduledAccountScope: isScheduledView ? accountScope : null,
       selectedMailbox: isScheduledView ? VIRTUAL_SCHEDULED_MAILBOX_ID : leavingScheduled ? "" : state.selectedMailbox,
       selectedEmail: leavingScheduled ? null : state.selectedEmail,
-      selectedEmailIds: leavingScheduled ? new Set<string>() : state.selectedEmailIds,
+      selectedEmailKeys: leavingScheduled ? new Set<string>() : state.selectedEmailKeys,
       // Search is unavailable in the scheduled view (the input is disabled there).
       // Reset any active search when entering it so a stale query can't linger or
       // re-run when the user leaves again.
@@ -4837,7 +4866,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
       await client.deleteEmail(emailId);
       set(state => ({
         selectedEmail: state.selectedEmail?.id === emailId ? null : state.selectedEmail,
-        selectedEmailIds: new Set(Array.from(state.selectedEmailIds).filter(id => id !== emailId)),
+        selectedEmailKeys: dropFromSelection(state, e => e.id === emailId),
       }));
     }
     if (get().pendingUndoSend?.submissionId === submissionId) {
@@ -4857,7 +4886,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
       await client.deleteEmail(email.id);
       set(state => ({
         selectedEmail: state.selectedEmail?.id === email.id ? null : state.selectedEmail,
-        selectedEmailIds: new Set(Array.from(state.selectedEmailIds).filter(id => id !== email.id)),
+        selectedEmailKeys: dropFromSelection(state, e => e.id === email.id),
       }));
       await get().fetchScheduledEmails(client);
       return null;
@@ -4907,7 +4936,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
       await client.deleteEmail(pending.emailId);
       set(state => ({
         selectedEmail: state.selectedEmail?.id === pending.emailId ? null : state.selectedEmail,
-        selectedEmailIds: new Set(Array.from(state.selectedEmailIds).filter(id => id !== pending.emailId)),
+        selectedEmailKeys: dropFromSelection(state, e => e.id === pending.emailId),
       }));
     } else if (pending.emailId) {
       const mailboxes = get().mailboxes.length > 0 ? get().mailboxes : await client.getMailboxes();