I can't seem to find any information on what IP I should be using for the webmail.yourdomain sub-domain. Is it the same as my main domain?
its just the same as watever domain or subdomain you have set up and are using for the email address.
$97 DISCOUNT with [color=#CC0000]DISCOM97[/color]More codes
If you ever want to start tracking this down, start with the DNS A records:https://panel.dreamhost.com/index.cgi?tree=domain.manage&
Then click DNS for your domain.
p.s. webmail is definitely different from your website/main domain.
It would appear that it's not the same IP, I tried this and it didn't work.
It should be noted that dreamhost is not my DNS provider, so this stuff isn't being handled for me by the system.
Even if DreamHost isn't your DNS, it should still act like it is if you're hosting your site here. Did you try looking at DNS in the panel?
Another approach would be to log into the command line and type:host webmail.MYDOMAIN.COMand that'll give you the IP address.