Our standard CPanel method of accessing the webmail is to use http://{domain}/webmail, which connects on ports 2095/2096.
Assuming your domain name is webmailuser.co.uk you would access the choices of webmail packages :
CPanel Webmail (Horde, Squirell, Neo) at http://www.webmailuser.co.uk/webmail
If you would prefer to access webmail through a dedictaed subdomain - such as webmail.domain straight to the Horde system you ...
- in cPanel set up a subdomain "webmail"
- setup redirection for that subdomain to
"https://www.webmailuser.co.uk:2096/horde/index.php//"
(change webmailuser.co.uk to your domain name)
This bypasses the usual domain/webmail selection of application and takes you straight to Horde, alternatively replace the /horde/ in the above example with your chosen webmail package.
How-To provided courtesy of Roger Cornwell, http://www.cornwell.nu