I have an EC2 running Ubuntu with Kafka installed, I've installed mailutils on the server because I have a script monitoring diskspace on the box and to email me when it reaches a certain threshold eg: 80%.

The Kafka server I've locked down to internal use, if I open all the ports on my outbound security group I can receive the warning from the script to my email.

I would like to lock this down to a port number on my outbound security group but can't seem to do it, I've tried ports 465 and 587. I have looked around online but nothing I found to do what I need, does anyone know what port it is?

  • 1
    Possible duplicate of What ports to open for mail server? – Ryan Babchishin Sep 21 '16 at 17:07
  • Not sure why it a duplicate, mine is to do with AWS EC2 security group. Should I edit the title more? – Gman Sep 21 '16 at 17:16
  • @RyanBabchishin Does Postfix use the destination ports as the outbound ports? – Paul Sep 22 '16 at 2:29
  • @Paul SMTP servers will usually connect to other servers on port 25, if that's what you mean. Because SMTP servers listen on that port. – Ryan Babchishin Sep 22 '16 at 3:58
  • @RyanBabchishin I read his question as configuring outbound ports, which are usually not the same as destination ports. – Paul Sep 22 '16 at 4:07

You're probably looking for TCP port 25.


SMTP by default uses TCP port 25. The protocol for mail submission is the same, but uses port 587. SMTP connections secured by SSL, known as SMTPS, default to port 465 (nonstandard, but sometimes used for legacy reasons).

| improve this answer | |
  • Duplicate of serverfault.com/questions/149903/… – Ryan Babchishin Sep 21 '16 at 17:07
  • Why duplicate, this is specific to AWS EC2 – Gman Sep 21 '16 at 17:13
  • @Gman Not really. AWS has a firewall... this is about opening ports in a firewall. AWS/pfSense/iptables... makes no difference, it's the same answer, same issue. – Ryan Babchishin Sep 22 '16 at 3:52
  • I will remove the question then – Gman Sep 23 '16 at 9:05
  • @Gman You don't need to do that (unless you want to). Your question hasn't been voted closed, which means not enough people agree with my opinion that this is a duplicate. Also, if the answer doesn't work and there is some EC2 specific problem to resolve, you can update your question and get help. I'll retract my vote/comments in that case. Did you try allowing port 25? – Ryan Babchishin Sep 23 '16 at 15:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.