Virtual server accounts with AT&T/Comcast internet connections unable to send e-mail

Some of the virtual servers in my installation have users with internet connections from AT&T/Comcast. Seemingly that company has implemented new firewall rules that prohibit SMTP on port 25.

I need some explicit instructions on what to change where and what directions to provide those users, without affecting the majority of my virtual servers and users who don't have this issue.

And of course the clients with the issue are getting extremely upset, and while they don't blame me, they blame AT&T/Comcast, they've also got to have the situation resolved or they'll need to switch hosts. Hence this lament and plea for your kind and efficient assistance.

Same platform access info as #4441.

Status: 
Closed (fixed)