1) First check the domain name which is hosted on the Windows hosting server by using following file
cat/var/qmail/control/rcpthosts
domain1.com
domain2.com
domain3.com
domain4.com
domain5.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/smtproutes
3) Then add the new ip address in the following format.
domain1.com:192.168.xx.1
domain2.com:192.168.xx.1
4) Save the file and restart qmail
/etc/init.d/qmail restart
Note: Please replace the “192.168.xx.1” to original ip address and the “yourdomain.com” equal the original domain name.