Mail sent to the wrong Office 365 region. ATTR35

New Contributor



I hope everyone is healthy and well.


My company uses an on premises Exchange Server to send and receive email for "" domain. This server is in place for several years without problems.


Recently we've started receiving "Mail sent to the wrong Office 365 region. ATTR35" errors when trying to send email to domain "". Delivery to other domains works flawlessly.


We do not have any Office 365 subscription and never had, but we've made a trial a few years ago.


Why are we getting theses errors? What can I do to solve this?


Any help would be greatly appreciated.


Thank you very much.



2 Replies
How are you sending those messages, if you have a connector in place this might be the reason, as detailed here:

@Vasil Michev


Our Exchange server has an "Outboud ti Office 365" connector but it's disabled. Then only enabled connector is the "Internet" Connector.


This shouldn't be a problem.