Exchange 2013 - "Mail sent to the wrong Office365 region. ATTR35"

36584367 201 Reputation points
2021-04-16T10:29:18.57+00:00

Hi. We have Exchange 2013 and all of a sudden we cannot reach SOME recipients that use Office365. On our Exchange we are getting an error saying "Mail sent to the wrong Office365 region. ATTR35". Any idea what this could be please? Thanks

Exchange | Exchange Server | Management
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  1. Andy David - MVP 158K Reputation points MVP Volunteer Moderator
    2021-04-21T12:04:33.153+00:00

    Interesting that each of these have multiple mx records and both have issues. I don't think this is your problem, I think its on them to fix.

    In both examples they have mx records that are not valid any longer.

    basmalta-com.mail.eo.outlook.com is wrong and not supported anymore, it should be set to the correct mx record for their domain in 365. ( the eo. part)

    in the second example, the mx record with a preference of 10 is invalid. Its possible your server is attempting to send to that secondary MX record.

    can you contact them and let them know? :)

    otherwise, this is not on you to fix.. you can point them to: https://learn.microsoft.com/en-us/exchange/troubleshoot/email-delivery/wrong-office-365-region-exo


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  1. Andy David - MVP 158K Reputation points MVP Volunteer Moderator
    2021-04-16T11:40:09.077+00:00
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  2. 36584367 201 Reputation points
    2021-04-16T11:42:31.697+00:00

    Hi AndyDavid,

    Yes I saw this post already but did not manage to follow. I opened a ticket with Microsoft and they are seeing to this. Thanks


  3. Lucas Liu-MSFT 6,191 Reputation points
    2021-04-19T06:23:17.587+00:00

    Hi @MatthewVassallo-0389 ,
    All these users in the same Office 365 tenant?
    Did you send the email directly without going through any equipment from Exchange?
    Dis you change any Exchange settings before this issue occurred?

    1. If possible, please share the complete NDR information with us.Please note that covering your personal information.
    2. As Andy said, please check if the recipient’s MX record is correct.
    3. Please try to send an email to these user mailboxes from other mailboxes.

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