Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

OK so this is driving me crazy.

Running sendmail on CentOS. It's running, and listening on 25:

[root@mysqlslavebackup ~]# nmap -sS -O -sV

Starting Nmap 4.11 ( ) at 2013-03-21 10:46 PDD<br>
Interesting ports on localhost.localdomain (<br>
Not shown: 1665 closed ports<br>
22/tcp    open  ssh               OpenSSH 4.3 (protocol 2.0)<br>
25/tcp    open  smtp              Sendmail 8.13.8/8.13.8<br>
53/tcp    open  domain<br>
111/tcp   open  rpc<br>
631/tcp   open  ipp               CUPS 1.2<br>
739/tcp   open  rpc<br>
953/tcp   open  rndc?<br>
3306/tcp  open  mysql             MySQL 5.5.11-enterprise-commercial-advanced-log<br>
5901/tcp  open  vnc               VNC (protocol 3.8)<br>
5902/tcp  open  vnc               VNC (protocol 3.8)<br>
5903/tcp  open  vnc               VNC (protocol 3.8)<br>
6001/tcp  open  X11                (access denied)<br>
6002/tcp  open  X11                (access denied)<br>
6003/tcp  open  X11                (access denied)<br>

I can telnet to 25 from the localhost, but from any other machine it appears the port is closed. iptables are off, and even if they were in I have an entry to open the port.

Can't for the life of me figure out what the heck it would be other than the fact this used to be a Zimbra mail server, but it has been uninstalled and there's no record of it in port bindings.

Any input would be awesome! Thanks!

share|improve this question

marked as duplicate by Kenny Rasschaert, dunxd, mdpc, Ward, Jenny D Mar 29 '13 at 9:12

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

It could be blocked at the network firewall, or as answer posted by Michael suggests, Sendmail may not be listening on the public network interface. – Stefan Lasiewski Mar 21 '13 at 18:28
Please post the output of lsof -i -P | grep sendmail. By default for CentOS sendmail only listens on localhost. – Mark Wagner Mar 21 '13 at 18:58
@MarkWagner netstat -ant| grep :25 gives tcp 0 0* LISTEN – Christopher Glenn Schlägel Mar 21 '13 at 21:16
It is only listening on loopback. Andrzej's answer is correct. – Mark Wagner Mar 21 '13 at 22:14

Why can't I receive external mail/incoming SMTP connections? [Sendmail and other MTA servers]

Are you sure your sendmail does not listen ONLY on loopback interface? []
It is default configuration on quite a few distributions.

You may use netstat -ant| grep :25 to chek it.

Sendail FAQ 4.22: Why can't I receive external mail?
In short: You may need to comment out DAEMON_OPTIONS line with in your and recompile it into

share|improve this answer
To rebuild and recompile in CentOS, after you edit you run /etc/mail/make followed by a service sendmail restart. – adamo Mar 21 '13 at 22:26

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