I have a customer who used to get their email via Exchange server. They've left their email provider, and I now have them set up in Outlook using IMAP.
Before the switch I exported their Exchange email to a PST.
I removed the Exchange account, and added the PST of exported email. Send/receive seems to work for all domains except his own. When I try to send an email to anyone on his own domain, I get a send/receive error of 0x80040201. I repaired all PSTs using ScanPST. No difference.
I figured out that if I remove the old exported Exchange PST file, it works fine. Having that PST file in Outlook is causing a problem.
I created a new empty PST, added it as a data file. Removed the old PST of exported Exchange mail. Ran Outlook and imported the old email into the new empty PST. No difference.
Anyone encountered this? I've never seen this kind of issue before.