Using a different Mailserver (MX)

If you want to use a different mailserver for some domain(s) have a look at some threads in the forum linked below.

Note: This also may help you if you get one of those errors:

postfix/virtual[19405]: E260688A63: to=<user@domain.tld>, relay=virtual, delay=0.27, delays=0.05/0.04/0/0.18, dsn=5.1.1, status=bounced (unknown user: "user@domain.tld")

change it for all domains:

Here´s a howto for setting a different MX for all domains. It modifies the template of ISP-CP:
http://www.isp-control.net/forum/thread-3661.html

change it for a single domain:

Have a look at this post. It describes how to take a domain out of the postfix configuration:
http://www.isp-control.net/forum/thread-3247.html