I don't mean to piggy back on your post LumbermanSVO but I recently switched to a Mac (Mac mail), same OS and cannot get my domain email working. At one point I got it to download messages, but only once and I cannot send. I've tried port 25 and 26.
and mail.domain.com as incoming and outgoing
I used to be able to smtp my isp's settings for outgoing and it worked, but isp has changed to routing through Gmail and not sure if that was a windows only workaround.
It asks for "Enter the password for user “username+domain.com” on SMTP s