A message stuck in Outlook Outbox usually points to offline mode, a connection problem, an attachment that is too large, a bad recipient address, or account settings that need repair.
Does this affect you?
Use this for Outlook for Microsoft 365 and Outlook 2021 or 2019 on Windows or Mac with Microsoft 365, Exchange, IMAP, or POP accounts.
Check offline mode and connection
Start here because these fixes are fast.
- Open Send/Receive.
- If Work Offline is highlighted, click it to return online.
- Load a website to confirm the internet works.
- Click Send/Receive All Folders or press F9.
- Check Microsoft 365 service health if using Exchange Online or Microsoft 365.
Check the stuck message and account
Use this when Outlook is online but messages still will not leave.
- Open Outbox and check whether the message has a large attachment. Replace large files with a OneDrive or cloud link.
- Confirm recipient addresses are complete and valid.
- Drag the stuck message to Drafts, reopen it, and send again.
- For IMAP or POP accounts, verify outgoing SMTP server, port, encryption, and authentication settings.
- Run account Repair from Outlook Account Settings.
More control
Test security software
Outgoing mail scanning from third-party security tools can block Outlook. Test briefly, then add an exception if that is the cause.
Start in safe mode
Open Outlook in safe mode to rule out add-ins. If sending works there, disable add-ins one by one.
Compare new and classic Outlook
If new Outlook behaves differently with the account, switch to classic Outlook temporarily to isolate the problem.
Create a new profile
If webmail sends normally but desktop Outlook does not, a fresh Outlook profile on Windows often clears local corruption.
Sources
- Microsoft Support – Fix email delivery issues for error code 4.4.7 in Exchange Online (2025)
- Microsoft Support – Message stuck in Outbox (2025)
- Microsoft 365 Status – Service health dashboard (2026)