How to configure Qmail to use a specific IP address for outgoing email in Plesk?
Note: Plesk GUI provides the option to configure the outgoing IP address for the email when Postfix is installed instead of Qmail. Check Plesk documentation for more details.
Connect to the server via SSH
Create the file
/var/qmail/control/outgoingipand add the IP address:
# cat /var/qmail/control/outgoingip
Restart QMail service:
# service qmail restart