@BRIAN - I think yours is not a SmarterMail ISSUE.
Probably this is a Outlook issue.
In practice: Outlook as the VERY FIRST thing checks if the domain is registered on a Microsoft Online service.
So if you have registered your domain in a Microsoft Online service (Microsoft 365, Office 365, MS Exchange Online or whatever...), Outlook will continue to try to log in to Microsoft's servers and will never try to contact your SmarterMail server.
The problem is that even if you also unsubscribed from Microsoft, they DO NOT DELETE your registration (they just deactivate it, but Outlook still sees the reference...), so you will continue to see this error and not be able to connect to the your SmarterMail server...
Damn Microsoft...
To solve the problem, Windows registry entries must be modified which tell Outlook to NOT CHECK Microsoft's online servers ANYMORE.
unfortunately now I don't have at hand the details of what needs to be changed, but as soon as I'm in the office I'll see if I can send them to you...
If in the meantime some good soul (or a member of the SmarterTools team) has them at hand, please post them to help Brian!
Gabriele Maoret - Head of SysAdmins at SERSIS
Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)