
Hi Doublescotch, (by the way, you might want to pour one, this looks like it may give you a few grey hairs, LOL)
Welcome to PCHF. We have a wonderful team of techs here, and I am sure that they can help you troubleshoot this very frustrating situation.
This is definitely not my area of expertise, but I think I may have some questions that will help the gurus to help you.
First of all, what is the email base that you are trying to use?
Does the isp provider show that they are actually recieving these emails, or are they just "set up to forward them"?
Can you direct us to your old website, perhaps one of us can get help from one of their techs.
Does your server receive emails from other email addresses, in other words have you tried setting up a different account name pathway?
I will PM the Server Gurus, please have as much information available as possible, and keep an eye out for their posts. Most importantly, DON'T PANIC!

It's going to be OK!
Looking forward to your reply,
TTFN
LGW