diff --git a/web/src/components/app/contacts/ContactsTable.tsx b/web/src/components/app/contacts/ContactsTable.tsx
index 60f17511a..65383c2ba 100644
--- a/web/src/components/app/contacts/ContactsTable.tsx
+++ b/web/src/components/app/contacts/ContactsTable.tsx
@@ -990,6 +990,7 @@ const LEAD_META: Record<
     completed: { label: "Done", dot: "bg-indigo-500", text: "text-indigo-700", Icon: CheckIcon },
     replied: { label: "Replied", dot: "bg-emerald-500", text: "text-emerald-700", Icon: CornerUpLeftIcon },
     bounced: { label: "Bounced", dot: "bg-rose-500", text: "text-rose-600", Icon: AlertTriangleIcon },
+    failed: { label: "Failed", dot: "bg-rose-500", text: "text-rose-600", Icon: AlertTriangleIcon },
     unsubscribed: { label: "Unsubscribed", dot: "bg-slate-300", text: "text-slate-400", Icon: BanIcon },
 };
 
@@ -997,9 +998,16 @@ function LeadStatusPill({ lead }: { lead?: ContactCampaignProgress | null }) {
     const status: LeadStatus = lead?.status ?? "pending";
     const meta = LEAD_META[status];
     const Icon = meta.Icon;
+    // A failed lead carries the worker's reason; surface it on hover since the
+    // pill itself only has room for the word.
+    const title =
+        status === "failed" && lead?.failure_reason
+            ? `Could not send: ${lead.failure_reason}`
+            : undefined;
     return (
         <span
             className={`inline-flex items-center gap-1.5 text-[10.5px] font-medium uppercase tracking-[0.08em] ${meta.text}`}
+            title={title}
         >
             {status === "active" ? (
                 <span className="campaign-grid text-sky-600 shrink-0" aria-hidden />
@@ -1030,6 +1038,7 @@ function LeadProgressStrip({
             completed: 0,
             replied: 0,
             bounced: 0,
+            failed: 0,
             unsubscribed: 0,
         };
         for (const ct of contacts) c[ct.campaign_lead?.status ?? "pending"]++;
@@ -1045,6 +1054,7 @@ function LeadProgressStrip({
         { key: "replied", color: "bg-emerald-500" },
         { key: "pending", color: "bg-slate-300" },
         { key: "bounced", color: "bg-rose-400" },
+        { key: "failed", color: "bg-rose-500" },
         { key: "unsubscribed", color: "bg-slate-200" },
     ];
 
@@ -1069,6 +1079,7 @@ function LeadProgressStrip({
                 <StripChip dot="bg-emerald-500" label="Replied" n={counts.replied} />
                 <StripChip dot="bg-slate-300" label="Queued" n={counts.pending} />
                 <StripChip dot="bg-rose-400" label="Bounced" n={counts.bounced} />
+                {counts.failed > 0 && <StripChip dot="bg-rose-500" label="Failed" n={counts.failed} />}
                 <StripChip dot="bg-slate-300" label="Unsub" n={counts.unsubscribed} />
             </div>
             <div className="ml-auto flex items-center gap-2 text-[10.5px] text-slate-400 tabular-nums">
diff --git a/web/src/hooks/useRealtimeEvents.ts b/web/src/hooks/useRealtimeEvents.ts
index 353466646..524a297f9 100644
--- a/web/src/hooks/useRealtimeEvents.ts
+++ b/web/src/hooks/useRealtimeEvents.ts
@@ -171,6 +171,24 @@ export function useRealtimeEvents() {
         return
       }
 
+      // A user-addressed mailbox/send error (a compose or reply the worker
+      // could not send, a mailbox that needs re-authorizing). Nothing else
+      // would tell the user, so toast it, then refresh the mailbox views.
+      if (event === 'ERROR') {
+        const data = payload.data as Record<string, unknown> | undefined
+        const title =
+          typeof data?.title === 'string' && data.title
+            ? data.title
+            : (getString('message') ?? 'Something went wrong')
+        const detail = typeof data?.message === 'string' ? data.message : ''
+        toast.error(detail ? `${title}: ${detail}` : title, {
+          id: `email-error-${getString('task_id') ?? getString('email_id') ?? 'general'}`,
+          duration: 8000,
+        })
+        invalidate([['emails', 'list'], ['unibox']])
+        return
+      }
+
       if (includes('ACCOUNT', 'EMAIL_STATUS', 'EMAIL_ERROR', 'WARMUP')) {
         // ACCOUNT_SYNC_STATE: the mailbox's import finished or fair use
         // started/stopped holding it; the drawer's sync card refetches.
diff --git a/web/src/lib/api/models/app/contacts/Contact.ts b/web/src/lib/api/models/app/contacts/Contact.ts
index e90519ea6..b0f78532f 100644
--- a/web/src/lib/api/models/app/contacts/Contact.ts
+++ b/web/src/lib/api/models/app/contacts/Contact.ts
@@ -1,15 +1,17 @@
 import type MiniCampaign from "../campaigns/MiniCampaign";
 import type MiniCategory from "./MiniCategory";
 
-// LeadStatus mirrors models.ContactCampaignProgress.Status — a contact's
+// LeadStatus mirrors models.ContactCampaignProgress.Status, a contact's
 // processing state inside a single campaign. "completed" = every step sent, no
-// reply (done); "active" = some but not all steps sent (still processing).
+// reply (done); "active" = some but not all steps sent (still processing);
+// "failed" = the mailbox could not send a step after every retry.
 export type LeadStatus =
     | "pending"
     | "active"
     | "completed"
     | "replied"
     | "bounced"
+    | "failed"
     | "unsubscribed";
 
 // ContactCampaignProgress is set only on contacts returned by a single-campaign
@@ -25,6 +27,9 @@ export interface ContactCampaignProgress {
     // Label of the step the lead is on now (latest step sent). Empty when the
     // lead hasn't been contacted yet.
     current_step?: string;
+    // The worker's reason for the last failed send; set only when status is
+    // "failed".
+    failure_reason?: string;
 }
 
 export default interface Contact {