Previously used Exchange 2003. Installed Exchange 2010, moved mailboxes to 2010 and then migrated to Office 365. Redirected MX records, Purged mailboxes on Exchange 2010. Everything is working fine with one exception.
Devices/Software were still using Exchange 2003 to relay e-mail. I set up a new SMTP server and moved everything to use this. However, I still have one web service that is using Exchange 2003 to relay e-mail - I'm not a developer, I can't modify the code. I'm waiting on the developer to modify the code. In the meantime, messages that are sent from the web service, via Exchange 2003 to previously internal e-mail addresses are failing.
Error logs are pointing to an NDR being created:
A non-delivery report with a status code of 5.4.6 was generated for recipient rfc822;firstname.lastname@example.org (Message-ID <2079311841.1492.143330418
Cause: A forward loop was detected by the categorizer. This is a common hosting configuration problem caused when someone uses the provisioning tool to create a contact in one organization unit and creates a user in a different organization user that share the same e-mail address.
Solution: Verify that you do not have a user in organizational unit and a contact in a different organizational unit that have the same e-mail address.
The KB says I should clear "This exchange organization is responsible for all mail delivery to this address" box. But, unfortunately, I can't do that because it's the Primary SMTP address.
Any suggestions on how to fix this?