Setting up webmail.domain.com as default for new domains.

1) You'll need to setup the virtualhost for apache. This can be accomplished by adding a 2nd virtualhost along side the domains main one.

cd /usr/local/directadmin/data/templates
cp virtual_host.conf custom
cd custom

You'll need to edit the newly copied virtual_host.conf (or virtual_host2.conf if you're using apache 2) file and make the file look like (just add the blue to the end of whatever you currently have)

|?DOCROOT=`HOME`/domains/`DOMAIN`/public_html|
|?OPEN_BASEDIR_PATH=`HOME`/:/tmp:/usr/local/lib/php/|
<VirtualHost |IP|:80>
|CUSTOM|
|?CGI=ScriptAlias /cgi-bin/ `DOCROOT`/cgi-bin/|
  ServerName www.|DOMAIN|
  ServerAlias www.|DOMAIN| |DOMAIN| |SERVER_ALIASES|
  ServerAdmin |ADMIN|
  DocumentRoot |DOCROOT|
  |CGI|

  |USECANONICALNAME|

  User |USER|
  Group |GROUP|
  CustomLog /var/log/httpd/domains/|DOMAIN|.bytes bytes
  CustomLog /var/log/httpd/domains/|DOMAIN|.log combined
  ErrorLog /var/log/httpd/domains/|DOMAIN|.error.log

  <Directory |DOCROOT|>
    Options +Includes -Indexes
    php_admin_flag engine |PHP|
    php_admin_flag safe_mode |SAFE_MODE|
    php_admin_value sendmail_path '/usr/sbin/sendmail -t -i -f |USER|@|DOMAIN|'
|*if OPEN_BASEDIR="ON"|
    php_admin_value open_basedir |OPEN_BASEDIR_PATH|
|*endif|

  </Directory>
|HANDLERS|
|MIMETYPES|

</VirtualHost>
<VirtualHost |IP|:80>
  ServerName webmail.|DOMAIN|
  ServerAdmin |ADMIN|
  DocumentRoot /var/www/html/squirrelmail
  CustomLog /var/log/httpd/domains/|DOMAIN|.bytes bytes
  CustomLog /var/log/httpd/domains/|DOMAIN|.log combined
  ErrorLog /var/log/httpd/domains/|DOMAIN|.error.log
</VirtualHost>

Save and exit. Then run

echo "action=rewrite&value=httpd" >> /usr/local/directadmin/data/task.queue
/usr/local/directadmin/dataskq d

to rewrite the httpd.conf files.

2) You'll also need to setup the dns portition.

cd /usr/local/directadmin/data/templates
cp dns_a.conf custom
cd custom
echo "webmail=|IP|" >> dns_a.conf

This will setup the webmail A record for new dns zones. For existing dns zones, you'll have to manually add the webmail A record to point to the domains IP.