Lets show you how to change the mail relaying IP address of a domain to something other than the main qmail IP address.
If primary mail server ip address is blocked in any of the spam checker sites ( eg SORBS-SPAM, BARRACUDA etc) then there is only one solution, that is change the mail server ip address on the server.
Incase of cpanel linux servers, you can easily change the mail server ip address by editing /etc/mailips file.
In PLESK you can change the outgoing mail server ip address by using “/var/qmail/control/smtproutes” file.
1) first check the domain name which is hosted on the server by using following file
cat /var/qmail/control/rcpthosts example1.com
example2.com
example3.com
example4.com
example5.com
2) By default the “/var/qmail/control/smtproutes” file is not present on PLESK server, you need to create it.
vi /var/qmail/control/smtproutes3) Then add the new ip address in the following format.
example1.com:192.168.0.2
example2.com:192.168.0.2
4) Save the file and restart qmail
/etc/init.d/qmail restart