How you can fix the issue Easiest fix: double-check that the sender typed the correct address and that the recipient still ...

Office 365


How you can fix the issue
Easiest fix: double-check that the sender typed the correct address and that the recipient still exists.
Clear the sender's email AutoComplete cache and retype the correct address. (Read this article for details on how to do this in Outlook.)

If those steps don't work, you need to contact the recipient's email admin to fix the problem. This isn't an issue with your Office 365 organization.

Help the recipient admin fix the issue
If the steps in the NDR didn't work, the recipient's email system is probably having either MX record problems or email address directory issues. For tips on fixing the problem, see Status code 5.1.1 in Exchange Online and Office 365.

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