Port 25 blocked but Firewall is off

Question

OK so this is driving me crazy.

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

[root@mysqlslavebackup ~]# nmap -sS -O -sV 127.0.0.1

Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2013-03-21 10:46 PDD<br>
Interesting ports on localhost.localdomain (127.0.0.1):<br>
Not shown: 1665 closed ports<br>
PORT      STATE SERVICE           VERSION<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!

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 0 127.0.0.1:25 0.0.0.0:* 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

AnFi · Answer 1 · 2013-03-21T20:53:35.610

3

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? [127.0.0.1:25]
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 127.0.0.1 in your sendail.mc and recompile it into sendmail.cf.

edited Mar 21 '13 at 20:53

answered Mar 21 '13 at 20:00

AnFi

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

Port 25 blocked but Firewall is off

1 Answers1