Ok, here is EXACTLY what I did, and email is working. However, I would like to not have every new WHM or end-user have to do this, so tell me if I am thinking correctly or not. I have been using Google Apps for my tlds for over a year now. At Godaddy, I added 4 MX records from Google (priority 10,20,30,40) all pointing to @, which points to my server's public IP.
Now, back at ISPConfig, I made 4 mx records also. In your manual, using the debian based system, your example shows creating separate hosts for mail, db, server, etc. My system is not set-up this way. The only server running is webserver.example.com. So, I set this:
imap.example.com >>> (pointing to) webserver.example.com
pop.example.com >>> webserver.example.com
smtp.example.com >>> webserver.example.com
mail.example.com >>> webserver.example.com
A couple of questions. Number one, are these settings (above) for ISPConfig correct? Again, mail is working. Number two, I am trying to keep my server and services "branded" if you will. In other words, can new domains now just point to my server in the MX records? That was what I was trying (and still am) to do with my nameservers. I guess what I am trying to say is that I want everything to run through my server, except one thing alone (which isn't really a server issue), and that is to be the actual domain registrar, like GoDaddy or Enom.
I hope I am making sense. Thanks for all.