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Outlook app for Mac sending emails stay in outbox

Roger Jones 20 Reputation points
2026-06-11T11:20:38.6633333+00:00

I have a user who can use their MS365 outlook account to send & receive emails with & without attachments from their mobile device and using OWA.

But when using the Outlook app for Mac they can only receive emails. "Sent" emails end up in the Outbox and stay there, despite sync attempts.

How to fix the sending issue?

Outlook | MacOS | New Outlook for Mac | For business
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Answer accepted by question author

Gabriel-N 18,380 Reputation points Microsoft External Staff Moderator
2026-06-11T11:56:45.94+00:00

Hello @Roger Jones

Based on your description (it works in OWA and on mobile, but not in Outlook for Mac), this is likely a client-side issue on the Mac rather than anything related to the mailbox itself. Could you please confirm whether the user has already tried some basic troubleshooting steps, such as:

  • Ensuring Outlook is fully updated
  • Signing out and signing back in
  • Fully quitting and reopening Outlook
  • Switching to Legacy Outlook to test sending, then switching back
  • Resetting or re-adding the account in Outlook
  • Removing and re-adding the Outlook profile

Also, could you let me know which macOS version the user is on, along with the Outlook for Mac version? And do you happen to know when this issue first started?

Looking forward to your update

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