How to run SMTP on a different or additional port, in Linux with Plesk

How to run SMTP on a different or additional port in Linux with Plesk

For one reason or another some people like to run their SMTP service on a port other than the standard TCP port 25. Whether it’s to bypass their ISP’s firewall, provide a second instance of SMTP, or maybe just to be different.

This article will show you a simple way to do this on a Linux server running the Plesk control panel.

In ‘/etc/xinetd.d/’ there is a file called smtp_psa, you will need to copy this file to another filename (in this example I’ll use smtp2_psa).

In this new file, you will want to change the line:
’service smtp’ to ’service smtp2′

Once this is complete, you will need to modify your /etc/services file, and add the smtp2 service:
Simply copy/paste the existing smtp line and change the name and port (we’ll use port 26 in this example).

smtp2 26/tcp mail
smtp2 26/udp mail

Restart xinetd.
/etc/init.d/xinetd restart

Check to make sure the new port is now listening
# netstat -plunt |grep :26

That should return something similar to

tcp 0 0 0.0.0.0:26 0.0.0.0:* LISTEN 2345/xinetd

You can test this connection from the outside by trying to telnet to port 26 on the server.
From a linux shell or Windows command prompt enter

telnet 123.123.123.123 26

(be sure to replace 123.123.123.123 with your server’s real IP address)
If it’s successful it should return something similar to

Trying 123.123.123.123…
Connected to hostname.domain (123.123.123.123).
Escape character is ‘^]’.
220 hostname.domain.tld ESMTP

Enter ‘quit’ to quit the telnet session.

You will also need to modify the port in your mail client to use the new SMTP port.

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5 Responses to “How to run SMTP on a different or additional port in Linux with Plesk”

eLo Says:
January 13th, 2008 at 4:29 am
Awesome thanks too.
Eric Says:
January 15th, 2008 at 2:30 am
Prior to performing this fix, I can receive ALL emails fine, I just can’t send via port 25 (since my ISP blocks it!)

Post performing this fix: I can send ALL emails just fine, but I can no longer receive emails from outside my domain.

Any suggestions or tips on why after doing this I can’t receive emails from outside my domain?
David Says:
February 15th, 2008 at 3:29 am
Eric, you must have it listen on BOTH 25 AND the new port. Read the instructions a little closer.

Simply copy/paste the existing smtp line and change the name and port (we’ll use port 26 in this example).

Copy, then change
Greg Says:
April 1st, 2008 at 5:22 am
Thanks for the tip. Did everything, netstat reports listening not problem. QMail however is not responding on this port. Should something also be changed in the QMail config. I am using Plesk 8

Thanks.
Text to Screen Says:
May 15th, 2008 at 11:00 am
I’m running Red Hat Linux, and I can’t figure out where to change my SMTP Port as my ISP Blocks 25?

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How to run SMTP on a different or additional port in Linux with Plesk

5 Responses to “How to run SMTP on a different or additional port in Linux with Plesk”

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