How can I configure qmail to run on another port on my Plesk Linux server?

The smtp daemon for Qmail/Plesk is ran from Xinetd.

In /etc/xinetd.d/ you will see this:

[root@root xinetd.d]# ls -l smpt*
-rw-r—r— 1 root root 400 Jul 18 23:18 smtp_psa
-rw-r—r— 1 root root 401 Jul 18 23:18 smtps_psa
[root@root xinetd.d]#

The contents of the files:

[root@root xinetd.d]# cat smtp_psa

service smtp
{
        socket_type     = stream
        protocol        = tcp
        wait            = no
        disable         = no
        user            = root
        instances       = UNLIMITED
        server          = /var/qmail/bin/tcp-env
        server_args     = /usr/sbin/rblsmtpd -r bl.spamcop.net /var/qmail/bin/relaylock /var/qmail/bin/qmail-smtpd /var/qmail/bin/smtp_auth /var/qmail/bin/true /var/qmail/bin/cmd5checkpw /var/qmail/bin/true
}

Copy one of these files to another file called something like “smtp2_psa”, change the “service” name in the file, then add the service “smtp2” to /etc/services, corresponding to the NEW port number, such as 26.

[root@root xinetd.d]# cp smtp_psa smtp2_psa

Change the service line in the new file ‘smtp2_psa” to be this:

service smtp2
{
        socket_type     = stream
        protocol        = tcp
        wait            = no
        disable         = no
        user            = root
        instances       = UNLIMITED
        server          = /var/qmail/bin/tcp-env
        server_args     = /usr/sbin/rblsmtpd -r bl.spamcop.net /var/qmail/bin/relaylock /var/qmail/bin/qmail-smtpd /var/qmail/bin/smtp_auth /var/qmail/bin/true /var/qmail/bin/cmd5checkpw /var/qmail/bin/true
}

Edit /etc/services with your favorite editor and add the tcp and udp lines for this service the lines should look like this:

smtp2 26/tcp mail
smtp2 26/udp mail

After this restart xinetd:

[root@root xinetd.d]# /etc/init.d/xinetd restart
Stopping xinetd: [ OK ]
Starting xinetd: [ OK ]

And you should see smtp listening on ports 25, and 26:

[root@root xinetd.d]# netstat -anp | grep xinetd
****cut****
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 6989/xinetd
tcp 0 0 0.0.0.0:26 0.0.0.0:* LISTEN 6989/xinetd
****cut****
[root@root xinetd.d]#

Make the appropriate changes if you want to run this second service on a port other than 26.