diff --git a/components/calendar/calendar-app.tsx b/components/calendar/calendar-app.tsx
index 211a641f8..f674984c0 100644
--- a/components/calendar/calendar-app.tsx
+++ b/components/calendar/calendar-app.tsx
@@ -16,6 +16,7 @@ import { useEmailStore } from "@/stores/email-store";
 import { useSettingsStore } from "@/stores/settings-store";
 import { useIdentityStore } from "@/stores/identity-store";
 import { useAccountStore } from "@/stores/account-store";
+import { useAccountSecurityStore } from "@/stores/account-security-store";
 import { usePolicyStore } from "@/stores/policy-store";
 import { toast } from "@/stores/toast-store";
 import { useIsDesktop, useIsMobile } from "@/hooks/use-media-query";
@@ -59,7 +60,7 @@ import { ShareCollectionDialog } from "@/components/settings/share-collection-di
 import { ConfirmDialog } from "@/components/ui/confirm-dialog";
 import { useConfirmDialog } from "@/hooks/use-confirm-dialog";
 import { CreateCalendarModal } from "@/components/calendar/create-calendar-modal";
-import { getUserParticipantId } from "@/lib/calendar-participants";
+import { getUserParticipantId, collectUserCalendarAddresses } from "@/lib/calendar-participants";
 import { generateBirthdayEvents, createBirthdayCalendar, BIRTHDAY_CALENDAR_ID } from "@/lib/birthday-calendar";
 import { sharedCalendarColorKey, pickUnusedCalendarColor } from "@/lib/shared-calendar-colors";
 import { debug } from "@/lib/debug";
@@ -106,7 +107,7 @@ export function CalendarApp({ linkSegments }: CalendarAppProps = {}) {
     fetchCalendars, fetchEvents, createEvent, updateEvent, deleteEvent, rsvpEvent,
     setSelectedDate, setViewMode, toggleCalendarVisibility, updateCalendar, shareCalendar,
     removeCalendar, clearCalendarEvents,
-    refreshAllSubscriptions, icalSubscriptions,
+    refreshAllSubscriptions, icalSubscriptions, isSubscriptionCalendar,
   } = useCalendarStore();
   const calendarEnabled = usePolicyStore((s) => s.isFeatureEnabled('calendarEnabled'));
   const { firstDayOfWeek, timeFormat, showWeekNumbers, enableCalendarTasks, showTasksOnCalendar, calendarHoverPreview, showBirthdayCalendar, birthdayCalendarColor, updateSetting } = useSettingsStore();
@@ -119,9 +120,21 @@ export function CalendarApp({ linkSegments }: CalendarAppProps = {}) {
   const contacts = useContactStore((s) => s.contacts);
   const normalizedViewMode = isCalendarViewMode(viewMode) ? viewMode : "month";
 
-  const currentUserEmails = useMemo(() =>
-    identities.map(id => id.email).filter(Boolean),
-    [identities]
+  // Aliases live on the principal, not on identities; fetch them so an
+  // alias-organized event is recognised as the user's own (see isOrganizer).
+  const accountEmails = useAccountSecurityStore((s) => s.emails);
+  const fetchPrincipal = useAccountSecurityStore((s) => s.fetchPrincipal);
+  const principalFetchedRef = useRef(false);
+  useEffect(() => {
+    if (principalFetchedRef.current) return;
+    principalFetchedRef.current = true;
+    if (accountEmails.length > 0) return; // already loaded elsewhere
+    void fetchPrincipal();
+  }, [accountEmails, fetchPrincipal]);
+
+  const currentUserEmails = useMemo(
+    () => collectUserCalendarAddresses(identities.map(id => id.email), accountEmails),
+    [identities, accountEmails]
   );
 
   const [showEventModal, setShowEventModal] = useState(false);
@@ -1553,6 +1566,7 @@ export function CalendarApp({ linkSegments }: CalendarAppProps = {}) {
                 onClose={() => { setShowEventModal(false); setEditEvent(null); setPendingPreview(null); setDefaultCalendarIdForCreate(undefined); setDefaultModalAllDay(false); }}
                 onPreviewChange={setPendingPreview}
                 currentUserEmails={currentUserEmails}
+                isSubscriptionCalendar={isSubscriptionCalendar}
                 isMobile={false}
               />
             </div>
@@ -1662,6 +1676,7 @@ export function CalendarApp({ linkSegments }: CalendarAppProps = {}) {
           onMouseEnter={() => { if (hoverTimerRef.current) { clearTimeout(hoverTimerRef.current); hoverTimerRef.current = null; } }}
           onMouseLeave={handleHoverLeave}
           currentUserEmails={currentUserEmails}
+          isSubscriptionCalendar={isSubscriptionCalendar}
           timeFormat={timeFormat}
           isMobile={isMobile}
         />
@@ -1682,6 +1697,7 @@ export function CalendarApp({ linkSegments }: CalendarAppProps = {}) {
           onRsvp={handleRsvp}
           onClose={() => { setShowEventModal(false); setEditEvent(null); setDefaultCalendarIdForCreate(undefined); setDefaultModalAllDay(false); }}
           currentUserEmails={currentUserEmails}
+          isSubscriptionCalendar={isSubscriptionCalendar}
           isMobile={true}
         />
       )}
diff --git a/components/calendar/event-detail-popover.tsx b/components/calendar/event-detail-popover.tsx
index bfc613bd4..d0b0389bf 100644
--- a/components/calendar/event-detail-popover.tsx
+++ b/components/calendar/event-detail-popover.tsx
@@ -15,11 +15,11 @@ import { parseDuration, getEventColor } from "./event-card";
 import { getEventDisplayEndDate, getEventEndDate, getEventStartDate } from "@/lib/calendar-utils";
 import { buildRecurrenceSummary } from "./recurrence-editor";
 import {
-  isOrganizer,
   getUserParticipantId,
   getUserStatus,
   getParticipantList,
 } from "@/lib/calendar-participants";
+import { getEventEditability } from "@/lib/calendar-editability";
 import { useFormatEventDate } from "@/hooks/use-format-event-date";
 
 interface EventDetailPopoverProps {
@@ -35,6 +35,7 @@ interface EventDetailPopoverProps {
   onMouseEnter?: () => void;
   onMouseLeave?: () => void;
   currentUserEmails?: string[];
+  isSubscriptionCalendar?: (calendarId: string) => boolean;
   timeFormat?: "12h" | "24h";
   isMobile?: boolean;
 }
@@ -120,6 +121,7 @@ export function EventDetailPopover({
   onMouseEnter,
   onMouseLeave,
   currentUserEmails = [],
+  isSubscriptionCalendar,
   timeFormat = "24h",
   isMobile,
 }: EventDetailPopoverProps) {
@@ -156,15 +158,17 @@ export function EventDetailPopover({
   const recurrenceLabel = useMemo(() => getRecurrenceLabel(event, t, locale), [event, t, locale]);
   const alertLabel = useMemo(() => getAlertLabel(event, t), [event, t]);
 
-  const userIsOrganizer = useMemo(() => {
-    if (!event.participants) return true;
-    return isOrganizer(event, currentUserEmails);
-  }, [event, currentUserEmails]);
-
-  const isAttendeeMode = useMemo(() => {
-    if (!event.participants) return false;
-    return !event.isOrigin && !userIsOrganizer;
-  }, [event, userIsOrganizer]);
+  // Gate affordances on calendar rights, not identity (see calendar-editability).
+  const editability = useMemo(() => {
+    const calendarsById = new Map(calendar ? [[calendar.id, calendar]] : []);
+    return getEventEditability(event, {
+      calendarsById,
+      userCalendarAddresses: currentUserEmails,
+      isSubscriptionCalendar: isSubscriptionCalendar ?? (() => false),
+    });
+  }, [event, calendar, currentUserEmails, isSubscriptionCalendar]);
+  const canEditBody = editability === "editable";
+  const rsvpMode = editability === "rsvp-only";
 
   const userParticipantId = useMemo(
     () => getUserParticipantId(event, currentUserEmails),
@@ -195,14 +199,14 @@ export function EventDetailPopover({
       const tag = target?.tagName?.toLowerCase();
       if (tag === "input" || tag === "textarea" || tag === "select") return;
       if (target?.getAttribute("contenteditable") === "true") return;
-      if (e.key === "e" && !noteExpanded) {
+      if (e.key === "e" && !noteExpanded && canEditBody) {
         e.preventDefault();
         onEdit();
       }
     };
     window.addEventListener("keydown", handleKey);
     return () => window.removeEventListener("keydown", handleKey);
-  }, [onClose, onEdit, noteExpanded]);
+  }, [onClose, onEdit, noteExpanded, canEditBody]);
 
   useEffect(() => {
     const handleClickOutside = (e: MouseEvent) => {
@@ -483,7 +487,7 @@ export function EventDetailPopover({
       </div>
 
       {/* Quick Note */}
-      {!isAttendeeMode && (
+      {canEditBody && (
         <div className="px-4 py-2 border-t border-border">
           {noteExpanded ? (
             <div className="space-y-2">
@@ -533,7 +537,7 @@ export function EventDetailPopover({
       )}
 
       {/* RSVP Bar (for attendees) */}
-      {isAttendeeMode && onRsvp && userParticipantId && (
+      {rsvpMode && onRsvp && userParticipantId && (
         <div className="px-4 py-3 border-t border-border">
           <p className="text-xs font-medium text-muted-foreground mb-2">
             {t("participants.rsvp_label")}
@@ -608,10 +612,12 @@ export function EventDetailPopover({
           </div>
         ) : (
           <>
-            <Button variant="default" size="sm" onClick={onEdit} className="h-7 text-xs">
-              <Pencil className="w-3.5 h-3.5 me-1" />
-              {t("events.edit")}
-            </Button>
+            {canEditBody && (
+              <Button variant="default" size="sm" onClick={onEdit} className="h-7 text-xs">
+                <Pencil className="w-3.5 h-3.5 me-1" />
+                {t("events.edit")}
+              </Button>
+            )}
             <Button
               variant="ghost"
               size="sm"
@@ -623,15 +629,17 @@ export function EventDetailPopover({
               {t("events.duplicate")}
             </Button>
             <div className="flex-1" />
-            <Button
-              variant="ghost"
-              size="sm"
-              onClick={() => setShowDeleteConfirm(true)}
-              className="h-7 text-xs text-red-600 dark:text-red-400"
-              title={t("events.delete")}
-            >
-              <Trash2 className="w-3.5 h-3.5" />
-            </Button>
+            {canEditBody && (
+              <Button
+                variant="ghost"
+                size="sm"
+                onClick={() => setShowDeleteConfirm(true)}
+                className="h-7 text-xs text-red-600 dark:text-red-400"
+                title={t("events.delete")}
+              >
+                <Trash2 className="w-3.5 h-3.5" />
+              </Button>
+            )}
           </>
         )}
       </div>
diff --git a/components/calendar/event-modal.tsx b/components/calendar/event-modal.tsx
index 5e0cfc145..b7f947ca5 100644
--- a/components/calendar/event-modal.tsx
+++ b/components/calendar/event-modal.tsx
@@ -19,6 +19,7 @@ import {
   getStatusCounts,
   buildParticipantMap,
 } from "@/lib/calendar-participants";
+import { getEventEditability, canCreateEventsIn } from "@/lib/calendar-editability";
 import { PluginSlot } from "@/components/plugins/plugin-slot";
 import { useSettingsStore } from "@/stores/settings-store";
 import { generateUUID } from "@/lib/utils";
@@ -48,6 +49,7 @@ interface EventModalProps {
   onClose: () => void;
   onPreviewChange?: (preview: PendingEventPreview | null) => void;
   currentUserEmails?: string[];
+  isSubscriptionCalendar?: (calendarId: string) => boolean;
   isMobile?: boolean;
 }
 
@@ -177,6 +179,7 @@ export function EventModal({
   onClose,
   onPreviewChange,
   currentUserEmails = [],
+  isSubscriptionCalendar,
   isMobile = false,
 }: EventModalProps) {
   const t = useTranslations("calendar");
@@ -193,10 +196,18 @@ export function EventModal({
     return isOrganizer(event, currentUserEmails);
   }, [event, currentUserEmails]);
 
-  const isAttendeeMode = useMemo(() => {
-    if (!event || !event.participants) return false;
-    return !event.isOrigin && !userIsOrganizer;
-  }, [event, userIsOrganizer]);
+  // Gate affordances on calendar rights, not identity (see calendar-editability).
+  const editability = useMemo(() => {
+    if (!event) return "editable" as const;
+    const calendarsById = new Map(calendars.map((c) => [c.id, c]));
+    return getEventEditability(event, {
+      calendarsById,
+      userCalendarAddresses: currentUserEmails,
+      isSubscriptionCalendar: isSubscriptionCalendar ?? (() => false),
+    });
+  }, [event, calendars, currentUserEmails, isSubscriptionCalendar]);
+  const canEditBody = editability === "editable";
+  const rsvpMode = editability === "rsvp-only";
 
   const userParticipantId = useMemo(() => {
     if (!event) return null;
@@ -261,8 +272,18 @@ export function EventModal({
     if (event?.calendarIds) return getPrimaryCalendarId(event) || calendars[0]?.id || "";
     if (defaultCalendarId && calendars.some(c => c.id === defaultCalendarId)) return defaultCalendarId;
     const defaultCal = calendars.find(c => c.isDefault);
-    return defaultCal?.id || calendars[0]?.id || "";
+    // Never default new events into a subscription / read-only calendar (#762).
+    return defaultCal?.id
+      || calendars.find(c => canCreateEventsIn(c, isSubscriptionCalendar))?.id
+      || calendars[0]?.id || "";
   });
+
+  // Calendars offered as create/move targets: writable, non-subscription, plus
+  // the event's current calendar so an in-place edit never blanks the select.
+  const selectableCalendars = useMemo(
+    () => calendars.filter(c => canCreateEventsIn(c, isSubscriptionCalendar) || c.id === calendarId),
+    [calendars, isSubscriptionCalendar, calendarId]
+  );
   const [recurrence, setRecurrence] = useState<RecurrenceOption>(() => {
     if (!event?.recurrenceRules?.length) return "none";
     const rule = event.recurrenceRules[0];
@@ -601,12 +622,12 @@ export function EventModal({
       }
       if ((e.ctrlKey || e.metaKey) && e.key === "Enter") {
         e.preventDefault();
-        if (!isAttendeeMode) handleSave();
+        if (canEditBody) handleSave();
       }
     };
     window.addEventListener("keydown", handleKey);
     return () => window.removeEventListener("keydown", handleKey);
-  }, [onClose, handleSave, isAttendeeMode, mode, isEdit]);
+  }, [onClose, handleSave, canEditBody, mode, isEdit]);
 
   useEffect(() => {
     const modal = modalRef.current;
@@ -634,7 +655,7 @@ export function EventModal({
 
   const hasParticipants = attendees.length > 0 || (event?.participants && Object.keys(event.participants).length > 0);
 
-  if (isAttendeeMode && event) {
+  if (rsvpMode && event) {
     const startD = getEventStartDate(event);
     const endD = getEventEndDate(event);
     const locationName = event.locations ? Object.values(event.locations)[0]?.name : null;
@@ -942,7 +963,7 @@ export function EventModal({
         {/* Action Bar */}
         <div className="px-6 py-3 border-t border-border flex-shrink-0 flex items-center justify-between">
           <div className="flex items-center gap-1">
-            {onDelete && (
+            {onDelete && canEditBody && (
               showDeleteConfirm ? (
                 <div className="flex items-center gap-2">
                   <span className="text-sm text-destructive">{t("form.delete_confirm")}</span>
@@ -967,7 +988,7 @@ export function EventModal({
               </Button>
             )}
           </div>
-          {!showDeleteConfirm && (
+          {!showDeleteConfirm && canEditBody && (
             <Button onClick={() => setMode("edit")}>
               <Pencil className="w-4 h-4 me-1" />
               {t("events.edit")}
@@ -1154,7 +1175,7 @@ export function EventModal({
             </div>
           )}
 
-          {calendars.length > 1 && (
+          {selectableCalendars.length > 1 && (
             <div>
               <label className="text-sm font-medium mb-1 block">{t("form.calendar_select")}</label>
               <select
@@ -1162,7 +1183,7 @@ export function EventModal({
                 onChange={(e) => setCalendarId(e.target.value)}
                 className="w-full rounded-md border border-input bg-background px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-ring"
               >
-                {calendars.map((cal) => (
+                {selectableCalendars.map((cal) => (
                   <option key={cal.id} value={cal.id}>
                     {cal.name}
                   </option>
diff --git a/lib/__tests__/calendar-editability.test.ts b/lib/__tests__/calendar-editability.test.ts
new file mode 100644
index 000000000..b1c7d5147
--- /dev/null
+++ b/lib/__tests__/calendar-editability.test.ts
@@ -0,0 +1,262 @@
+import { describe, it, expect } from 'vitest';
+import type { CalendarEvent, CalendarParticipant, CalendarRights } from '@/lib/jmap/types';
+import {
+  getEventEditability,
+  canCreateEventsIn,
+  eventHasNoOwner,
+  type EventEditability,
+  type EditabilityContext,
+} from '@/lib/calendar-editability';
+
+function makeEvent(overrides: Partial<CalendarEvent> = {}): CalendarEvent {
+  return {
+    '@type': 'Event',
+    id: 'ev1',
+    uid: 'uid-ev1',
+    calendarIds: { cal1: true },
+    title: 'Test Event',
+    description: '',
+    descriptionContentType: 'text/plain',
+    start: '2026-03-01T10:00:00',
+    duration: 'PT1H',
+    timeZone: 'UTC',
+    showWithoutTime: false,
+    status: 'confirmed',
+    freeBusyStatus: 'busy',
+    privacy: 'public',
+    keywords: null,
+    categories: null,
+    color: null,
+    recurrenceId: null,
+    recurrenceIdTimeZone: null,
+    recurrenceRules: null,
+    recurrenceOverrides: null,
+    excludedRecurrenceRules: null,
+    useDefaultAlerts: false,
+    alerts: null,
+    locations: null,
+    virtualLocations: null,
+    links: null,
+    relatedTo: null,
+    utcStart: null,
+    utcEnd: null,
+    isDraft: false,
+    isOrigin: true,
+    sequence: 0,
+    created: '2026-03-01T09:00:00Z',
+    updated: '2026-03-01T09:00:00Z',
+    locale: null,
+    replyTo: null,
+    organizerCalendarAddress: null,
+    participants: null,
+    mayInviteSelf: false,
+    mayInviteOthers: false,
+    hideAttendees: false,
+    ...overrides,
+  };
+}
+
+function makeRights(overrides: Partial<CalendarRights> = {}): CalendarRights {
+  return {
+    mayReadFreeBusy: false,
+    mayReadItems: false,
+    mayWriteAll: false,
+    mayWriteOwn: false,
+    mayUpdatePrivate: false,
+    mayRSVP: false,
+    mayShare: false,
+    mayDelete: false,
+    ...overrides,
+  };
+}
+
+const ALL_RIGHTS = makeRights({
+  mayReadFreeBusy: true, mayReadItems: true, mayWriteAll: true, mayWriteOwn: true,
+  mayUpdatePrivate: true, mayRSVP: true, mayShare: true, mayDelete: true,
+});
+const READ_ONLY = makeRights({ mayReadFreeBusy: true, mayReadItems: true });
+const WRITE_OWN = makeRights({
+  mayReadFreeBusy: true, mayReadItems: true, mayWriteOwn: true, mayUpdatePrivate: true, mayRSVP: true,
+});
+const RSVP_ONLY = makeRights({
+  mayReadFreeBusy: true, mayReadItems: true, mayUpdatePrivate: true, mayRSVP: true,
+});
+
+const SELF = 'alice@example.com';
+const ALIAS = 'info@example.com';
+const OTHER = 'carol@example.com';
+
+const owner = (email: string): Partial<CalendarParticipant> => ({
+  '@type': 'Participant', name: email, email, roles: { owner: true, attendee: true },
+  sendTo: { imip: `mailto:${email}` }, participationStatus: 'accepted', kind: 'individual',
+});
+const attendee = (email: string): Partial<CalendarParticipant> => ({
+  '@type': 'Participant', name: email, email, roles: { attendee: true },
+  sendTo: { imip: `mailto:${email}` }, participationStatus: 'needs-action', kind: 'individual',
+});
+
+/** Build a context whose single calendar `cal1` carries the given rights. */
+function ctx(
+  rights: CalendarRights | null,
+  addresses: string[] = [SELF],
+  subscriptions: string[] = [],
+): EditabilityContext {
+  const calendarsById = new Map(rights ? [['cal1', { myRights: rights }]] : []);
+  return {
+    calendarsById,
+    userCalendarAddresses: addresses,
+    isSubscriptionCalendar: (id) => subscriptions.includes(id),
+  };
+}
+
+describe('canCreateEventsIn (issue #762)', () => {
+  const sub = (id: string) => id === 'sub';
+  it('allows a writable, non-subscription calendar', () => {
+    expect(canCreateEventsIn({ id: 'c', myRights: ALL_RIGHTS }, sub)).toBe(true);
+    expect(canCreateEventsIn({ id: 'c', myRights: WRITE_OWN }, sub)).toBe(true);
+  });
+  it('rejects a read-only calendar', () => {
+    expect(canCreateEventsIn({ id: 'c', myRights: READ_ONLY }, sub)).toBe(false);
+    expect(canCreateEventsIn({ id: 'c', myRights: RSVP_ONLY }, sub)).toBe(false);
+  });
+  it('rejects an iCal subscription even when its Stalwart rights are writable', () => {
+    expect(canCreateEventsIn({ id: 'sub', myRights: ALL_RIGHTS }, sub)).toBe(false);
+  });
+  it('is permissive when myRights is absent (local/birthday calendars)', () => {
+    expect(canCreateEventsIn({ id: 'c', myRights: undefined as never }, sub)).toBe(true);
+  });
+});
+
+describe('eventHasNoOwner', () => {
+  it('is true for a plain event with no participants/organizer', () => {
+    expect(eventHasNoOwner(makeEvent())).toBe(true);
+  });
+  it('is false when an owner-role participant exists', () => {
+    expect(eventHasNoOwner(makeEvent({ participants: { a: owner(SELF) } as never }))).toBe(false);
+  });
+  it('is false when an event-level organizer address exists', () => {
+    expect(eventHasNoOwner(makeEvent({ organizerCalendarAddress: `mailto:${OTHER}` }))).toBe(false);
+  });
+  it('is false when a reply destination exists', () => {
+    expect(eventHasNoOwner(makeEvent({ replyTo: { imip: `mailto:${OTHER}` } }))).toBe(false);
+  });
+  it('is true when only non-owner participants exist', () => {
+    expect(eventHasNoOwner(makeEvent({ participants: { b: attendee(OTHER) } as never }))).toBe(true);
+  });
+});
+
+describe('getEventEditability - calendar rights gate', () => {
+  it('mayWriteAll -> editable even when the user is not the organizer', () => {
+    const ev = makeEvent({ isOrigin: false, organizerCalendarAddress: `mailto:${OTHER}`,
+      participants: { a: owner(OTHER), b: attendee(SELF) } as never });
+    expect(getEventEditability(ev, ctx(ALL_RIGHTS))).toBe('editable');
+  });
+
+  it('read-only calendar -> read-only even for an event the user organizes', () => {
+    const ev = makeEvent({ organizerCalendarAddress: `mailto:${SELF}`,
+      participants: { a: owner(SELF) } as never });
+    expect(getEventEditability(ev, ctx(READ_ONLY))).toBe('read-only');
+  });
+
+  it('mayWriteOwn + user is organizer -> editable', () => {
+    const ev = makeEvent({ participants: { a: owner(SELF), b: attendee(OTHER) } as never });
+    expect(getEventEditability(ev, ctx(WRITE_OWN))).toBe('editable');
+  });
+
+  it('mayWriteOwn + user is a mere attendee -> rsvp-only (cannot edit body)', () => {
+    const ev = makeEvent({ isOrigin: false, organizerCalendarAddress: `mailto:${OTHER}`,
+      participants: { a: owner(OTHER), b: attendee(SELF) } as never });
+    expect(getEventEditability(ev, ctx(WRITE_OWN))).toBe('rsvp-only');
+  });
+
+  it('mayWriteOwn + ownerless event -> editable', () => {
+    const ev = makeEvent({ participants: { b: attendee(SELF) } as never });
+    expect(getEventEditability(ev, ctx(WRITE_OWN))).toBe('editable');
+  });
+
+  it('RSVP-only rights + participant -> rsvp-only', () => {
+    const ev = makeEvent({ isOrigin: false, organizerCalendarAddress: `mailto:${OTHER}`,
+      participants: { a: owner(OTHER), b: attendee(SELF) } as never });
+    expect(getEventEditability(ev, ctx(RSVP_ONLY))).toBe('rsvp-only');
+  });
+
+  it('RSVP-only rights + user is NOT a participant -> read-only', () => {
+    const ev = makeEvent({ isOrigin: false, organizerCalendarAddress: `mailto:${OTHER}`,
+      participants: { a: owner(OTHER), b: attendee('dave@example.com') } as never });
+    expect(getEventEditability(ev, ctx(RSVP_ONLY))).toBe('read-only');
+  });
+
+  it('no write / no rsvp rights -> read-only', () => {
+    const ev = makeEvent({ participants: { a: owner(SELF) } as never });
+    expect(getEventEditability(ev, ctx(READ_ONLY))).toBe('read-only');
+  });
+});
+
+describe('getEventEditability - subscription calendars', () => {
+  it('an event in a client-side iCal subscription is read-only regardless of rights/organizer', () => {
+    const ev = makeEvent({ organizerCalendarAddress: `mailto:${SELF}`,
+      participants: { a: owner(SELF) } as never });
+    // Even if the (irrelevant) rights map says all-writable, the subscription wins.
+    expect(getEventEditability(ev, ctx(ALL_RIGHTS, [SELF], ['cal1']))).toBe('read-only');
+  });
+});
+
+describe('getEventEditability - unknown calendar rights', () => {
+  it('own origin copy is editable when rights are not yet loaded', () => {
+    expect(getEventEditability(makeEvent({ isOrigin: true }), ctx(null))).toBe('editable');
+  });
+  it('a delivered (non-origin) copy stays read-only until rights load', () => {
+    expect(getEventEditability(makeEvent({ isOrigin: false }), ctx(null))).toBe('read-only');
+  });
+});
+
+describe('getEventEditability - alias over-permissiveness regression', () => {
+  it('organizer == account alias in a READ-ONLY shared calendar -> read-only (not editable)', () => {
+    // The alias branch would have matched isOrganizer and opened the editor; the
+    // rights gate must keep it read-only.
+    const ev = makeEvent({ isOrigin: false, organizerCalendarAddress: `mailto:${ALIAS}`,
+      participants: { a: owner(ALIAS) } as never });
+    expect(getEventEditability(ev, ctx(READ_ONLY, [SELF, ALIAS]))).toBe('read-only');
+  });
+
+  it('organizer == account alias in a WRITE-OWN calendar -> editable (legitimate alias edit)', () => {
+    const ev = makeEvent({ organizerCalendarAddress: `mailto:${ALIAS}`,
+      participants: { a: owner(ALIAS) } as never });
+    expect(getEventEditability(ev, ctx(WRITE_OWN, [SELF, ALIAS]))).toBe('editable');
+  });
+});
+
+describe('getEventEditability - multi-calendar membership', () => {
+  it('requires the right on EVERY calendar (a read-only member blocks edit)', () => {
+    const ev = makeEvent({ calendarIds: { cal1: true, cal2: true },
+      participants: { a: owner(SELF) } as never });
+    const context: EditabilityContext = {
+      calendarsById: new Map([
+        ['cal1', { myRights: ALL_RIGHTS }],
+        ['cal2', { myRights: READ_ONLY }],
+      ]),
+      userCalendarAddresses: [SELF],
+      isSubscriptionCalendar: () => false,
+    };
+    expect(getEventEditability(ev, context)).toBe('read-only');
+  });
+});
+
+describe('getEventEditability - matrix sanity', () => {
+  const cases: Array<[string, CalendarRights, boolean, EventEditability]> = [
+    ['writeAll/organizer', ALL_RIGHTS, true, 'editable'],
+    ['writeAll/attendee', ALL_RIGHTS, false, 'editable'],
+    ['writeOwn/organizer', WRITE_OWN, true, 'editable'],
+    ['writeOwn/attendee', WRITE_OWN, false, 'rsvp-only'],
+    ['rsvpOnly/attendee', RSVP_ONLY, false, 'rsvp-only'],
+    ['readOnly/organizer', READ_ONLY, true, 'read-only'],
+    ['readOnly/attendee', READ_ONLY, false, 'read-only'],
+  ];
+  it.each(cases)('%s -> %s', (_label, rights, userIsOrganizer, expected) => {
+    const ev = userIsOrganizer
+      ? makeEvent({ participants: { a: owner(SELF), b: attendee(OTHER) } as never })
+      : makeEvent({ isOrigin: false, organizerCalendarAddress: `mailto:${OTHER}`,
+          participants: { a: owner(OTHER), b: attendee(SELF) } as never });
+    expect(getEventEditability(ev, ctx(rights))).toBe(expected);
+  });
+});
diff --git a/lib/__tests__/calendar-participants.test.ts b/lib/__tests__/calendar-participants.test.ts
index 341410a61..0b287ae5a 100644
--- a/lib/__tests__/calendar-participants.test.ts
+++ b/lib/__tests__/calendar-participants.test.ts
@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest';
 import type { CalendarEvent, CalendarParticipant } from '@/lib/jmap/types';
 import {
   isOrganizer,
+  collectUserCalendarAddresses,
   getUserParticipantId,
   getUserStatus,
   getParticipantList,
@@ -179,6 +180,56 @@ describe('isOrganizer', () => {
     event.organizerCalendarAddress = 'mailto:someoneelse@example.com';
     expect(isOrganizer(event, ['alice@example.com'])).toBe(false);
   });
+
+  // Regression: an event organized under one of the account's ALIAS addresses
+  // is still the user's own event and must be recognised as such (otherwise the
+  // calendar UI flips it to a read-only invite). The primary address alone does
+  // not match; the alias has to be part of the user's address list.
+  it('does NOT match an alias organizer when only the primary address is known', () => {
+    const event = makeEvent({ att1: attendeeParticipant });
+    event.organizerCalendarAddress = 'mailto:info@example.com'; // an account alias
+    expect(isOrganizer(event, ['alice@example.com'])).toBe(false);
+  });
+
+  it('matches an alias organizer once the alias is included in the address list', () => {
+    const event = makeEvent({ att1: attendeeParticipant });
+    event.organizerCalendarAddress = 'mailto:info@example.com';
+    const addresses = collectUserCalendarAddresses(['alice@example.com'], ['info@example.com']);
+    expect(isOrganizer(event, addresses)).toBe(true);
+  });
+
+  it('matches an alias owner participant once the alias is included', () => {
+    const event = makeEvent({
+      org: { ...orgParticipant, email: 'info@example.com', sendTo: { imip: 'mailto:info@example.com' } },
+    });
+    const addresses = collectUserCalendarAddresses(['alice@example.com'], ['INFO@example.com']);
+    expect(isOrganizer(event, addresses)).toBe(true);
+  });
+});
+
+describe('collectUserCalendarAddresses', () => {
+  it('merges identity and alias addresses', () => {
+    expect(collectUserCalendarAddresses(['alice@example.com'], ['info@example.com', 'sales@example.com']))
+      .toEqual(['alice@example.com', 'info@example.com', 'sales@example.com']);
+  });
+
+  it('de-duplicates case-insensitively, keeping the first-seen casing', () => {
+    expect(collectUserCalendarAddresses(['Alice@Example.com'], ['alice@example.com', 'INFO@example.com']))
+      .toEqual(['Alice@Example.com', 'INFO@example.com']);
+  });
+
+  it('drops empty, undefined and whitespace-only entries', () => {
+    expect(collectUserCalendarAddresses(['alice@example.com', '', '  ', undefined, null], []))
+      .toEqual(['alice@example.com']);
+  });
+
+  it('trims surrounding whitespace', () => {
+    expect(collectUserCalendarAddresses(['  alice@example.com  '], [])).toEqual(['alice@example.com']);
+  });
+
+  it('returns an empty array when given no addresses', () => {
+    expect(collectUserCalendarAddresses([], [])).toEqual([]);
+  });
 });
 
 describe('getUserParticipantId', () => {
diff --git a/lib/calendar-editability.ts b/lib/calendar-editability.ts
new file mode 100644
index 000000000..bfe8c9a97
--- /dev/null
+++ b/lib/calendar-editability.ts
@@ -0,0 +1,76 @@
+import type { CalendarEvent, Calendar, CalendarRights } from '@/lib/jmap/types';
+import { isOrganizer, getUserParticipantId } from '@/lib/calendar-participants';
+
+export type EventEditability = 'editable' | 'rsvp-only' | 'read-only';
+
+export interface EditabilityContext {
+  /** Viewer's calendars by id; only their `myRights` is read. */
+  calendarsById: ReadonlyMap<string, Pick<Calendar, 'myRights'>>;
+  /** Identities + aliases; only refines owner/participant detection, never the gate. */
+  userCalendarAddresses: string[];
+  /** Client-side external iCal (webcal/ICS) subscriptions - always read-only. */
+  isSubscriptionCalendar: (calendarId: string) => boolean;
+}
+
+/**
+ * Whether new events may be created in / moved into this calendar: writable and
+ * not a (read-only) iCal subscription. Bulwark subscriptions are real Stalwart
+ * calendars with writable myRights, so the flag must be checked too (issue #762).
+ */
+export function canCreateEventsIn(
+  calendar: Pick<Calendar, 'id' | 'myRights'>,
+  isSubscriptionCalendar?: (calendarId: string) => boolean,
+): boolean {
+  if (isSubscriptionCalendar?.(calendar.id)) return false;
+  const r = calendar.myRights;
+  return !r || r.mayWriteAll || r.mayWriteOwn;
+}
+
+/** Ownerless (plain, non-scheduled) events are editable under `mayWriteOwn`. */
+export function eventHasNoOwner(event: CalendarEvent): boolean {
+  if (event.organizerCalendarAddress) return false;
+  if (event.replyTo && Object.keys(event.replyTo).length > 0) return false;
+  if (event.participants) {
+    for (const p of Object.values(event.participants)) {
+      if (p.roles?.owner) return false;
+    }
+  }
+  return true;
+}
+
+/**
+ * Editability gated on the calendar's `myRights` FIRST, then identity - so
+ * read-only/subscription calendars stay read-only and an alias organizer can't
+ * over-open events the user can't write. (Stalwart: organizer identity does not
+ * confer calendar write; the ACL does.)
+ */
+export function getEventEditability(
+  event: CalendarEvent,
+  ctx: EditabilityContext,
+): EventEditability {
+  const calIds = Object.keys(event.calendarIds ?? {});
+
+  // Subscriptions have no write path and myRights can't describe them.
+  if (calIds.some((id) => ctx.isSubscriptionCalendar(id))) return 'read-only';
+
+  const rights = calIds
+    .map((id) => ctx.calendarsById.get(id)?.myRights)
+    .filter((r): r is CalendarRights => Boolean(r));
+
+  // Rights not loaded: allow only the user's own origin copy for now.
+  if (rights.length === 0) return event.isOrigin ? 'editable' : 'read-only';
+
+  // Every calendar must grant the right (a read-only member blocks edit).
+  const may = (k: keyof CalendarRights) => rights.every((r) => r[k]);
+  const isOwner =
+    isOrganizer(event, ctx.userCalendarAddresses) || eventHasNoOwner(event);
+
+  if (may('mayWriteAll')) return 'editable';
+  if (may('mayWriteOwn') && isOwner) return 'editable';
+
+  const isParticipant =
+    getUserParticipantId(event, ctx.userCalendarAddresses) != null;
+  if (may('mayRSVP') && isParticipant) return 'rsvp-only';
+
+  return 'read-only';
+}
diff --git a/lib/calendar-participants.ts b/lib/calendar-participants.ts
index fea07a6de..1f0d32434 100644
--- a/lib/calendar-participants.ts
+++ b/lib/calendar-participants.ts
@@ -62,6 +62,30 @@ export function getEventOrganizerEmails(event: CalendarEvent): string[] {
   return emails.filter(Boolean);
 }
 
+/**
+ * Merge the user's calendar addresses (identities + account aliases) so
+ * isOrganizer() recognises alias-organized events as the user's own. Identities
+ * alone carry only one address each, so an alias organizer looked foreign.
+ * De-duplicated case-insensitively (first casing kept); blanks dropped.
+ */
+export function collectUserCalendarAddresses(
+  ...groups: Array<ReadonlyArray<string | null | undefined>>
+): string[] {
+  const seen = new Set<string>();
+  const out: string[] = [];
+  for (const group of groups) {
+    for (const raw of group) {
+      const trimmed = raw?.trim();
+      if (!trimmed) continue;
+      const key = trimmed.toLowerCase();
+      if (seen.has(key)) continue;
+      seen.add(key);
+      out.push(trimmed);
+    }
+  }
+  return out;
+}
+
 export function isOrganizer(event: CalendarEvent, userEmails: string[]): boolean {
   if (userEmails.length === 0) return false;
   const lower = userEmails.map(e => e.toLowerCase());