How to change mail server ip address for qmail
1) first check the domain names which are configured on the server by viewing following file
cat /var/qmail/control/rcpthosts
domain1.com
domain2.com
domain3.com
domain4.com
domain5.com2) By default the “/var/qmail/control/smtproutes” file is not present on PLESK servers, so you need to create it.
vi /var/qmail/control/smtproutes
3) Then add the new ip addresses in the following format.
domain1.com:192.168.0.2
domain2.com:192.168.0.24) Then save the file and restart qmail
/etc/init.d/qmail restart