DH for www, godaddy for mail, mx records etc

Hi - I've got a client that wants to use godaddy to handle their existing email, but I'm moving the web stuff to dreamhost.

Here's the situation:

I'd like to alter the name servers so it points to dreamhost.
Then alter the mx records at DH so that it points back to godaddy's mail stuff:
pop.secureserver.net/ smtpout.secureserver.net

However at issue is that a large number of the users are using mail.theircompanydomainname.com as the pop server --which I believe is just a cname of pop.secureserver.net
if I do a dns lookup on mail.theircompanydomainname.com I get:

IP address: 64.202.165.92
Host name: pop.secureserver.net

Alias:
mail.theircompanydomainname.com
64.202.165.92 is from United States(US) in region North America



How do I route mail.theircompanydomainname.com via dreamhost or godaddy
so that it uses pop.secureserver.net without having all of those users change their settings.

Many thanks in advance,
Ben

It sounds like you're headed in the right direction. Here's how to change the MX:
http://wiki.dreamhost.com/Mx

I host my mail here, so the following is speculation:
Without mail hosted here, DreamHost won't set up mail.yourdomain.com and other such hostnames. You can use the DNS of your fully hosted domain to not only add your MX records, but add CNAMEs for mail.theircompanydomainname.com that point to pop.secureserver.net and smtp.theircompanydomainname.com pointing to smtpout.secureserver.net

-Scott