Hey Roger,
This issue has been fixed in the SmarterMail beta.
The issue was regarding sending via a domain alias using EM Client.
If you look at BETA Build 8440 which was released on 2/9/2023 it specifically mentions this issue as fixed.
If you're still having issues with this and are running beta 8440 or higher please open a new ticket regarding this issue.
I'm going to go ahead and mark this as fixed here but let me know if I'm wrong in doing so.
Kind Regards,
Zach Sylvester
Software Developer
SmarterTools Inc.
www.smartertools.com