diff --git a/hooks/use-mailbox-drop.ts b/hooks/use-mailbox-drop.ts
index 39bd7608..6ccf363e 100644
--- a/hooks/use-mailbox-drop.ts
+++ b/hooks/use-mailbox-drop.ts
@@ -173,7 +173,11 @@ export function useMailboxDrop({ mailbox, onDropComplete, onSuccess, onError }:
         // import call to target the owner's JMAP account.
         const jmapDestId = mailbox.originalId || mailbox.id;
         const destJmapOverride = mailbox.isShared ? mailbox.accountId : undefined;
-        await crossAccountMoveEmails(bySource, destAccountId, jmapDestId, destJmapOverride);
+        // Mirror image for the source: a shared group mailbox is accessed
+        // through the viewing user's client, but the email/blob live in the
+        // owner's JMAP account, so the copy/delete must target it.
+        const sourceJmapOverride = sourceMb?.isShared ? sourceMb.accountId : undefined;
+        await crossAccountMoveEmails(bySource, destAccountId, jmapDestId, destJmapOverride, sourceJmapOverride);
       } else {
         // Single-account or same-account-shared move: bulk JMAP request.
         await moveEmailsToMailbox(client, emailIds, mailbox.id);
diff --git a/lib/jmap/client-interface.ts b/lib/jmap/client-interface.ts
index 120717bd..f657cca9 100644
--- a/lib/jmap/client-interface.ts
+++ b/lib/jmap/client-interface.ts
@@ -97,7 +97,7 @@ export interface IJMAPClient {
   updateEmailKeywords(emailId: string, keywords: Record<string, boolean>): Promise<void>;
   setKeyword(emailId: string, keyword: string): Promise<void>;
   migrateKeyword(oldKeyword: string, newKeyword: string): Promise<number>;
-  deleteEmail(emailId: string): Promise<void>;
+  deleteEmail(emailId: string, accountId?: string): Promise<void>;
   moveToTrash(emailId: string, trashMailboxId: string, accountId?: string, markAsRead?: boolean): Promise<void>;
   batchDeleteEmails(emailIds: string[]): Promise<void>;
   batchMoveEmails(emailIds: string[], toMailboxId: string, accountId?: string, markAsRead?: boolean): Promise<void>;
@@ -210,8 +210,8 @@ export interface IJMAPClient {
           signal?: AbortSignal;
         },
   ): Promise<{ blobId: string; size: number; type: string }>;
-  getBlobDownloadUrl(blobId: string, name?: string, type?: string): string;
-  fetchBlob(blobId: string, name?: string, type?: string): Promise<Blob>;
+  getBlobDownloadUrl(blobId: string, name?: string, type?: string, accountId?: string): string;
+  fetchBlob(blobId: string, name?: string, type?: string, accountId?: string): Promise<Blob>;
   fetchBlobAsObjectUrl(blobId: string, name?: string, type?: string): Promise<string>;
   fetchBlobArrayBuffer(blobId: string, name?: string, type?: string): Promise<ArrayBuffer>;
   downloadBlob(blobId: string, name?: string, type?: string): Promise<void>;
diff --git a/lib/jmap/client.ts b/lib/jmap/client.ts
index da36121c..87a92416 100644
--- a/lib/jmap/client.ts
+++ b/lib/jmap/client.ts
@@ -1271,10 +1271,10 @@ export class JMAPClient implements IJMAPClient {
     return allIds.length;
   }
 
-  async deleteEmail(emailId: string): Promise<void> {
+  async deleteEmail(emailId: string, accountId?: string): Promise<void> {
     await this.request([
       ["Email/set", {
-        accountId: this.accountId,
+        accountId: accountId || this.accountId,
         destroy: [emailId],
       }, "0"],
     ]);
@@ -3117,21 +3117,23 @@ export class JMAPClient implements IJMAPClient {
     }
   }
 
-  getBlobDownloadUrl(blobId: string, name?: string, type?: string): string {
+  getBlobDownloadUrl(blobId: string, name?: string, type?: string, accountId?: string): string {
     if (!this.downloadUrl) {
       throw new Error('Download URL not available. Please reconnect.');
     }
 
-    // RFC 6570 level 1 URI template expansion
+    // RFC 6570 level 1 URI template expansion. Blobs are scoped per account,
+    // so a caller fetching a blob from a delegated/shared account must pass
+    // that owner's accountId rather than defaulting to the primary one.
     return this.downloadUrl
-      .replace('{accountId}', encodeURIComponent(this.accountId))
+      .replace('{accountId}', encodeURIComponent(accountId || this.accountId))
       .replace('{blobId}', encodeURIComponent(blobId))
       .replace('{name}', encodeURIComponent(name || 'download'))
       .replace('{type}', encodeURIComponent(type || 'application/octet-stream'));
   }
 
-  async fetchBlob(blobId: string, name?: string, type?: string): Promise<Blob> {
-    const url = this.getBlobDownloadUrl(blobId, name, type);
+  async fetchBlob(blobId: string, name?: string, type?: string, accountId?: string): Promise<Blob> {
+    const url = this.getBlobDownloadUrl(blobId, name, type, accountId);
     const response = await this.authenticatedFetch(url, {});
     if (!response.ok) {
       throw new Error(`Failed to fetch blob: ${response.status}`);
diff --git a/stores/email-store.ts b/stores/email-store.ts
index 4da028a9..e19895c4 100644
--- a/stores/email-store.ts
+++ b/stores/email-store.ts
@@ -152,12 +152,17 @@ interface EmailStore {
    * for the import — used when dropping into a delegated/shared mailbox that
    * is owned by a different JMAP account but accessed through the same
    * client (i.e. there is no separate connected client for the owner).
+   * `sourceJmapAccountId` is the mirror image for the source side: when the
+   * emails live in a delegated/shared mailbox accessed through the source
+   * client, the copy/delete must target the owner's JMAP account rather than
+   * the source client's primary one.
    */
   crossAccountMoveEmails: (
     emailIdsBySource: Map<string, string[]>,
     destAccountId: string,
     destMailboxId: string,
     destJmapAccountId?: string,
+    sourceJmapAccountId?: string,
   ) => Promise<void>;
   searchEmails: (client: IJMAPClient, query: string) => Promise<void>;
   advancedSearch: (client: IJMAPClient) => Promise<void>;
@@ -1233,7 +1238,7 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
     }
   },
 
-  crossAccountMoveEmails: async (emailIdsBySource, destAccountId, destMailboxId, destJmapAccountId) => {
+  crossAccountMoveEmails: async (emailIdsBySource, destAccountId, destMailboxId, destJmapAccountId, sourceJmapAccountId) => {
     if (emailIdsBySource.size === 0) return;
     set({ isLoading: true, error: null });
     try {
@@ -1260,14 +1265,17 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
         // the source clean in the happy path.
         const results = await Promise.allSettled(
           emailIds.map(async (emailId) => {
-            const full = await sourceClient.getEmail(emailId);
+            // When the source is a delegated/shared mailbox, the email,
+            // its blob, and the destroy all live in the owner's JMAP
+            // account, not the source client's primary one.
+            const full = await sourceClient.getEmail(emailId, sourceJmapAccountId);
             if (!full?.blobId) {
               throw new Error('Source email has no raw blob to copy');
             }
-            const blob = await sourceClient.fetchBlob(full.blobId);
+            const blob = await sourceClient.fetchBlob(full.blobId, undefined, undefined, sourceJmapAccountId);
             const keywords: Record<string, boolean> = { ...(full.keywords ?? {}) };
             await destClient.importRawEmail(blob, { [destMailboxId]: true }, keywords, destJmapAccountId);
-            await sourceClient.deleteEmail(emailId);
+            await sourceClient.deleteEmail(emailId, sourceJmapAccountId);
             return emailId;
           }),
         );