I am using smart_host and it(mail.myotherdomain.com) is listening on PORT 26

I have put these two lines in my /etc/mail/sendmail.mc

define(`RELAY_MAILER_ARGS', `TCP $h 26')dnl

I then do

make -C /etc/mail
service sendmail restart

Is there a way to verify that it is actually using port 26?


2 Answers 2


You can try to telnet to the box, using port 26.

telnet localhost 26

Then, issue some SMTP commands to test.


First, ensure something is listening on port 26:

$ sudo netstat -tunlp | grep 26

Then, if there is, from another host on your network, try and connect via telnet:

$ telnet <IP_address> 26

If sendmail answers, you're good.


Why do you want to do this? The email transport system is fairly rigid with regards to what ports SMTP happens on, and if you want a prayer of being able to interact with other mail systems, you have no choice but to have your MTA listening on port 25.

  • I thought the RELAY_MAILER_ARGS is setting it up to use a different port of the smarthost (mail.myotherdomain.com). what i am try to accomplish is send mail from this server via my mail server that has a port 26 that allows relaying from my Class C. So i am trying to test that the smarthost is sending out the rely to port 26. I hope that clarifies things alittle better
    – randy
    Commented Dec 9, 2013 at 21:57
  • Well if it's your own infrastructure, then use whatever ports you want. You do know, however, that classful addressing died 20 years ago, right?
    – EEAA
    Commented Dec 9, 2013 at 22:00
  • so any help or just snarkyness??
    – randy
    Commented Dec 9, 2013 at 22:16
  • Not trying to be snarky, just honest. No one uses classful addressing any more. My answer contains what you need to know to test whether or not sendmail is running on port 26, correct?
    – EEAA
    Commented Dec 9, 2013 at 22:19
  • thanks for the help. I know its listening on 26. I am using smarthost to rely to another server that is listening on 26. I am verify that the relay is leaving on 26
    – randy
    Commented Dec 10, 2013 at 0:49

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