MessageDeliveryFailedException: Could not deliver the message [len=70, Failure code: ad29 Using microsoft outlook for MAc

Joseph Colonna 0 Reputation points
2026-10-13T15:39:18.46+00:00

Outlook stopped working today. MessageDeliveryFailedException: Could not deliver the message, Failure code: ad29. I am using Outlook for Mac. All updates are made.

Outlook | MacOS | New Outlook for Mac | For home
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  1. Kai-H 28,525 Reputation points Microsoft External Staff Moderator
    2026-10-14T11:06:18.29+00:00

    Hi, Joseph Colonna

    Error ad29 is not a well-documented server code. Similar cases suggest that Outlook’s local message queue, cached account data, or the “Undo Send” delay can leave messages stuck even when the mailbox itself is working.

    Here are some suggestions you can try:

    Sign in to Outlook on the web and send a short test message to yourself. If this works, the mailbox is fine and the problem is limited to the Mac app.

    In Outlook for Mac, delete any unsent messages from Drafts and Outbox, then empty Deleted Items. Create a completely new message rather than resending or forwarding the failed one.

    Open Outlook > Settings > Composing and temporarily set Undo Send to Off. A stuck deferred-send state has caused messages to remain in Drafts until that state was cleared.

    If all messages still fail, remove the account from Outlook, restart the Mac, and add the account again using a fresh sign-in. This rebuilds the local account data.

    As a final test, create a temporary macOS user account and add Outlook there. If sending works, the issue is within the original Mac user profile rather than the mailbox.

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  2. AI answer

    2026-10-13T15:39:30.42+00:00

    For Outlook for Mac, this error can align with common send/receive failures. Work through these checks in order:

    1. Verify Outlook is online.
      • In Outlook, open the Outlook menu.
      • Make sure Work Offline is not checked.
    2. Confirm the Mac still has Internet access.
      • Open a web browser and verify websites load.
      • If on a managed network, also confirm the network is not blocking mail traffic.
    3. Check whether Microsoft cloud storage is full.
      • If cloud storage is full, Outlook for Mac may not be able to send or receive email.
    4. Review the account credentials and server settings.
      • In Outlook, go to Tools > Accounts.
      • Select the affected account.
      • Verify the email address, user name, and password are correct.
      • If the mail provider requires special settings such as SSL or non-default ports, confirm those with the provider.
    5. If the account is POP or IMAP, enable SMTP authentication.
      • Go to Tools > Accounts.
      • Select the account.
      • Under Outgoing server, select More Options.
      • Choose the required authentication type and enter credentials if needed.
    6. If sending fails only on a specific network, check for SMTP blocking.
      • Some ISPs or networks block connections to the outgoing mail server.
      • If that is happening, use an alternative SMTP server provided by the ISP or network administrator.
      • In Tools > Accounts, select the account and update the Outgoing server value.
    7. If the network uses a proxy server, confirm the proxy settings in macOS System Preferences.
    8. If the server was working previously and suddenly stopped, verify the mail server is available.
      • Contact the email provider or network administrator to confirm the server is online.

    If the failure happens only for certain recipients, review the delivery failure message for clues such as:

    • invalid or outdated recipient address
    • recipient mailbox full
    • message too large
    • temporary remote server timeout

    For postmaster or failed-delivery messages, check the Diagnostic information for administrators section in the returned message. That section usually identifies the delivery reason.

    AI-generated content may be incorrect. Read our transparency notes for more information.

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