Plesk alternative port for relaying

SMTP stands for Simple Mail Transfer Protocol, it was designed a long time ago when the Internet was a peaceful place. Today we are facing new challenges, so there should be new solutions.

One of the problem is SPAM messages, spammers are keeping to bombard us everyday with junk mails. We did invented black/white list to protect us from them.

If your clients are connecting from an ip address that’s listed in RBL lists (it’s not uncommon for ISPs that are using dynamic ip addresses) they can’t send messages through your server if you are using RBLs.

Disabling RBLs checks it’s not an option, we’ll configure an alternative port for relaying on port 1025 for the clients listed in RBLs.

You can just copy your smtp_psa file and customize it:

cd /etc/xinetd.d/
cp smtp_psa smtp_alt_psa
vim smtp_alt_psa

You need to change service name from smtp to smtp-alt and remove rblsmptd command and it’s -r parameters, finally it should something like this:

# /etc/xinetd.d/smtp_alt_psa
service smtp-alt
{
        socket_type     = stream
        protocol        = tcp
        wait            = no
        disable         = no
        user            = root
        instances       = UNLIMITED
        server          = /var/qmail/bin/tcp-env
        server_args     = -Rt0 /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
}

Append the new service to /etc/services:

smtp-alt        1025/tcp        
smtp-alt        1025/udp

And restart the xinetd service:

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

Verify your configuration with telnet command:

[root@sirius xinetd.d]# telnet localhost 1025
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
220 sirius.example.net ESMTP
 
# Ctr+] and quit to exit telnet

Now, instruct your clients to change port in SMTP settings from 25 to 1025, they will be able to send mails through your server even you are using RBL lists.