i've set up DNS records for http://webmail.mydomain.co.uk/ and told cPanel where it should go, but Apache or something isn't picking it up - it just goes to the (previous) first domain, www.somethingelse.co.uk, and displays the homepage.

How can I see what's going wrong and where? it's really starting to annoy me, as there seems to be no reason why it's not functioning.

Apache has this that cpanel's inserted:

Code:
<VirtualHost *.*.*.*:80>
    ServerAlias www.webmail.mydomain.co.uk
    ServerAlias webmail.mydomain.co.uk
    ServerAdmin webmaster@mydomain.co.uk
    DocumentRoot /home/user/subdomains/webmail
    ServerName webmail.mydomain.co.uk
    <IfModule mod_suphp.c>
        suPHP_UserGroup user user
    </IfModule>
    <IfModule !mod_disable_suexec.c>
        User user
        Group user
    </IfModule>
    BytesLog /usr/local/apache/domlogs/webmail.mydomain.co.uk-bytes_log
    CustomLog /usr/local/apache/domlogs/webmail.mydomain.co.uk combined
    ScriptAlias /cgi-bin/ /home/user/subdomains/webmail/cgi-bin/
</VirtualHost>
the bold line was added myself, and mimics how it was on my previous server (which worked).