diff --git a/packages/twenty-server/src/modules/messaging/message-folder-manager/drivers/imap/services/__tests__/imap-get-all-folders.service.spec.ts b/packages/twenty-server/src/modules/messaging/message-folder-manager/drivers/imap/services/__tests__/imap-get-all-folders.service.spec.ts
index f9cb244224..285cf6695e 100644
--- a/packages/twenty-server/src/modules/messaging/message-folder-manager/drivers/imap/services/__tests__/imap-get-all-folders.service.spec.ts
+++ b/packages/twenty-server/src/modules/messaging/message-folder-manager/drivers/imap/services/__tests__/imap-get-all-folders.service.spec.ts
@@ -190,5 +190,46 @@ describe('ImapGetAllFoldersService', () => {
       );
       expect(result.find((f) => f.isSentFolder)).toBeUndefined();
     });
+
+    it.each([['\\Noselect'], ['\\NoSelect'], ['\\NOSELECT'], ['\\noselect']])(
+      'should treat %s as non-selectable (RFC 3501 attribute names are case-insensitive)',
+      async (flagSpelling) => {
+        const mailboxList = [
+          createMockMailbox({ path: 'INBOX' }),
+          createMockMailbox({
+            path: 'Shared Folders',
+            flags: new Set([flagSpelling]),
+          }),
+          createMockMailbox({
+            path: 'Shared Folders/team/INBOX',
+            name: 'INBOX',
+            parentPath: 'Shared Folders/team',
+          }),
+        ];
+
+        mockImapClient.list.mockResolvedValue(mailboxList);
+        mockImapClient.status.mockImplementation(async (path: string) => {
+          if (path === 'Shared Folders') {
+            throw new Error(`Mailbox doesn't exist: ${path}`);
+          }
+
+          return { uidValidity: BigInt(1) } as any;
+        });
+
+        const result = await service.getAllMessageFolders(
+          CONNECTED_ACCOUNT,
+          MESSAGE_CHANNEL,
+        );
+
+        expect(mockImapClient.status).not.toHaveBeenCalledWith(
+          'Shared Folders',
+          expect.anything(),
+        );
+
+        const paths = result.map((f) => f.externalId?.split(':')[0]);
+
+        expect(paths).not.toContain('Shared Folders');
+      },
+    );
   });
 });
diff --git a/packages/twenty-server/src/modules/messaging/message-folder-manager/drivers/imap/services/imap-get-all-folders.service.ts b/packages/twenty-server/src/modules/messaging/message-folder-manager/drivers/imap/services/imap-get-all-folders.service.ts
index 669948b68d..975f7d34b5 100644
--- a/packages/twenty-server/src/modules/messaging/message-folder-manager/drivers/imap/services/imap-get-all-folders.service.ts
+++ b/packages/twenty-server/src/modules/messaging/message-folder-manager/drivers/imap/services/imap-get-all-folders.service.ts
@@ -138,7 +138,21 @@ export class ImapGetAllFoldersService implements MessageFolderDriver {
   }
 
   private isMailboxSelectable(mailbox: ListResponse): boolean {
-    return !mailbox.flags?.has('\\Noselect');
+    // Per RFC 3501, IMAP attribute names are case-insensitive. Different
+    // servers vary the spelling (Dovecot: \Noselect, Stalwart: \NoSelect),
+    // so we compare lowercased to avoid attempting SELECT on a virtual
+    // namespace placeholder, which the server would reject as NONEXISTENT.
+    if (!mailbox.flags) {
+      return true;
+    }
+
+    for (const flag of mailbox.flags) {
+      if (flag.toLowerCase() === '\\noselect') {
+        return false;
+      }
+    }
+
+    return true;
   }
 
   private isValidMailbox(