When you transfer the domain it'll take 24-48 hrs for the information to propagate around the world ... Wherever you transferred it to you should have a control panel (or bind server on your server) to add subdomains etc.
I would explain in more detail but im late for work.
OK I had another look in Sendmail settings and they look just fine to me. I think that the problem is with the BIND settings, actually they don't point to sendmail. Actually when I put in my browser mail.dvd-guides.com the mp3-guides.com frontpage comes up!
EDIT: I changed some settings in Sendmail and now the mail program replies that there is a POP3 error and not that "Connection is refused".
It was bind, you had all of your domains pointing to existing domains [which forced redundant lookups for the same ip], so i changed things around a bit, made a few shortcuts here and there, hopefully everything will work the way it should.
I'll have a go at that mp3-guides.com error.
EDIT Just don't pay attention to it most people don't try to browse to their email servers
mail seems to work fine, i managed to login via telnet to your account, what errors do ya get? :S
I don't know, they where the default settings made by VirtualMin, so I guess they were correct. What I can't find is the port settings.
Sendmail had a PORT=stmp,ADDRESS=127.0.0.0 setting which I changed to PORT=110 and ADDRESS=(my IP). After that the "Connection refused" message changed to "POP3" error.
The problem is that mail.dvd-guides.com goes to 64.251.10.180:80 (Apache) and not 64.251.10.180:110 (Sendmail) or at least that's what I think the problem is, with my limited knowledge. Shouldn't there be a setting that would say that mail.dvd-guides.com reads port 110, ftp.dvd-guides.com reads port 21 and so on?