We are using Google Apps for our email service. Obviously people can login at gmail.google.com but we'd like to set up mail.domain.com to work as well. Obviously I can do this in Apache with a redirect, but would prefer a DNS solution so as not to hit our server unnecessarily.
Adding a CNAME record is one of the things that are required to use a custom domain name for a Google Apps service such as Gmail (in this case, it should point to ghs.googlehosted.com instead of gmail.google.com).
You also need to let Google Apps know about it so that they can redirect the domain name properly. See Customize a Google Apps service address - Google Apps Administrator Help.
I'm after trying a CNAME record but the http request is redirected to the region specific Google search page :(
mail.domain.com CNAME gmail.google.com