Undeliverable message and also failure to get new emails. Original Failure code: ad29

Joseph Colonna 0 Reputation points
2026-10-13T15:48:11.34+00:00
  1. Sending mail from webmail works, from outlook on mobile as well. What should I do next?

Failure code: ad29
Outlook | Windows | New Outlook for Windows | For business
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  1. Ruby Nguyen 3,130 Reputation points Independent Advisor
    2026-10-13T16:19:28.93+00:00

    Good day Joseph, 

    Just to gently clarify before going any further, this forum is separate from Microsoft Support. I don’t have the ability to access or investigate individual accounts because this is a user‑to‑user support forum.  

    Since you can send email successfully from Outlook on the web and Outlook mobile, your mailbox and the Exchange Online mail service appear to be working, and the issue is likely related to the Outlook desktop client. The ad29 error shown in similar cases is associated with a message failing to be delivered from Outlook. 

    Here are some steps you can follow: 

    Step 1: Sync the mailbox 

    Open New Outlook. 

    Select View > Sync. 

    Wait for the sync to finish. 

    Send a test email to yourself and check whether it appears in both Sent Items and Inbox. 

    Step 2: Refresh the sign in session 

    Open Settings > Accounts > Your accounts. 

    Select Manage for the affected account. 

    If prompted, sign in again and complete authentication. 

    Restart New Outlook and test email sending and receiving. 

    Step 3: Remove and re-add the account 

    Open Settings > Accounts > Your accounts. 

    Select Manage for the affected account, then select Remove. Repeat this process for all accounts currently configured in the New Outlook app.

    Restart New Outlook. 

    Select Add Account, sign in again and test email sending and receiving. 

    Removing the account only clears local cached data. It doesn't remove emails stored in your Microsoft 365 mailbox. 

    Step 4: Repair or reset New Outlook 

    Close New Outlook. 

    Open Windows Settings > Apps > Installed apps. 

    Find Outlook and select Advanced options. 

    Select Repair and test again. 

    If the issue continues, select Reset, reopen Outlook, add the account again if prompted, and test the mailbox. 

    Step 5: Reinstall New Outlook 

    Please uninstall the New Outlook desktop app, then reinstall it: Outlook for Windows - Free download and install on Windows | Microsoft Store 

    If you have any questions, please don’t hesitate to reach out at any time. 

    Thank you for your patience and understanding. 

    If you have any extra questions about this answer, please click "Comment".        

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  2. AI answer

    2026-10-13T15:48:28.5833333+00:00

    Since sending works in Outlook on the web and Outlook mobile, the next step is to focus on the Outlook client and the specific delivery failure details.

    1. Open the non-delivery report and scroll to Diagnostic information for administrators. That section usually shows the actual reason the message was rejected.
    2. If the recipient address was auto-completed in Outlook, delete it and re-enter the full address manually. A stale Auto-Complete entry can cause delivery failures.
    3. If the message had an attachment, reduce its size and resend. Outlook.com cannot send attachments larger than 25 MB, and some undeliverable cases can also occur with large attachments.
    4. If the message is going to many recipients, reduce the number of recipients and try again.
    5. If the error indicates the message was blocked or listed by a spam/blocklist filter, the recipient’s email provider support team must unblock the account or domain.
    6. If the message says mailbox full, quota exceeded, mailbox not found, invalid mailbox, user unknown, host unknown, or domain lookup failed, verify the address and confirm the recipient is still using that address.
    7. If the error is a temporary server issue such as connection timed out, message expired, no adequate servers, out of memory, or resources temporarily unavailable, wait a short time and resend.
    8. If Outlook on the web continues to work but the Windows Outlook client does not, try sending the same message from Outlook.com as a workaround while reviewing the desktop client configuration.

    For the problem of not getting new emails, check these Outlook.com conditions:

    1. Check the Other tab.
    2. Check the Junk Email folder and Junk Email settings.
    3. Restore sorting to Filter > Sort > Date.
    4. Check whether email forwarding is enabled.
    5. Check whether any email rules are moving or hiding messages.
    6. If using a third-party mail service with Outlook Mobile or Desktop, make sure it supports modern authentication and IMAP. If IMAP or POP are active and causing issues, disable IMAP and POP and test again.

    If a specific sender’s messages are missing and there is no visible error, ask that sender to review Sender Support in Outlook.com.

    The code ad29 is not explained in the available documentation, so the actionable next step is to use the full non-delivery report details rather than the short code alone.

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

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