So currently checking a user's account whos been getting Non-Delivery Reports for emails he hasn't been sending himself or replying to himself. This is caused by publicity email coming into his mailbox which appears to trigger some sort of autoreply to this mail address firstname.lastname@example.org.
The user's main method of access to his mail is via his Ipad and iPhone. He does have a windows machine which in the first instance I believe was the culprit, but he doesn't have any email clients there. Whenever he needs to use the laptop he logs in via OWA from his browser and he pretty much never really uses the machine.
From within Office 365 admin and exchange consoles, I don't see anything that would be set to forward emails or autoreply to specific ones. We have already reset the account's password and it still keeps happening.
Does anyone have an idea of what other things to check to avoid this happening?
For now, I have set a mail flow route targetted at this recipient so the user doesn't get the NDR emails while we try to dig up was is actually happening.