topic Re: mailx port in Operating System - Linux

mailx port

Martin Johnson — Fri, 23 Apr 2010 12:37:07 GMT

I have a script that checks to see if an application is running. If the application is not running it uses mailx to send a message that the application is down. Unfortunately, the messages are not being received. I'm sure it is a firewall issue. My problem is I don't know which port mailx uses, so I don't know which port to open.

Ten points for the right answer!

Marty

Re: mailx port

Steven Schweda — Fri, 23 Apr 2010 13:07:18 GMT

SMTP normally uses port 25.

> [...] I'm sure [...]

Because ...?

You can run a simple test using Telnet to see
if there's some obvious problem. Something
like:

telnet server_system 25

(A suitable Web search should reveal how to
send an actual e-mail message that way, too.)

Re: mailx port

Martin Johnson — Fri, 23 Apr 2010 13:24:46 GMT

Unfortunately, telnet has been disabled in this environment.

Marty

Re: mailx port

Steven Schweda — Fri, 23 Apr 2010 13:29:35 GMT

> Unfortunately, telnet has been disabled in
> this environment.

What, exactly, does that mean? Disabling the
Telnet service on some system does not
normally affect anyone's ability to run a
Telnet client program, especially when one
is not using the normal Telnet port (and/or
one is doing it on some other system).

> telnet server_system 25

Did you actually _try_ this, or is this
another case of "I'm sure" without any actual
evidence?

Re: mailx port

Matti_Kurkela — Fri, 23 Apr 2010 13:54:19 GMT

A traditional mailx binary does not use network at all. Instead, it does some pre-processing and then invokes "/usr/sbin/sendmail" (= the local MTA, which actually may be Exim, Postfix, Qmail or something else) in one-shot mode to actually send the message.

You should view the mail logs of your system to see what happens to the message you tried to send with mailx. Usually this log is at /var/log/mail.log.

If it's a firewall issue, then the messages might still be in the local outgoing mail queue: use the "mailq" command to view the mail queue status.

When the local MTA attempts to deliver outgoing mail, it normally uses the SMTP protocol, which uses TCP port 25 as standard. If SMTP-over-SSL is configured for some particular mail destination, TCP port 465 might also be used, but this is somewhat uncommon.

MK

Re: mailx port

Martin Johnson — Fri, 23 Apr 2010 14:13:10 GMT

Steven,

When I try to telnet I get this:

telnet localhost 25
Trying 127.0.0.1...
telnet: connect to address 127.0.0.1: Connection refused
telnet: Unable to connect to remote host: Connection refused

Marty

Re: mailx port

Martin Johnson — Fri, 23 Apr 2010 14:29:30 GMT

Matti,

/var/log/maillog has the following entry after I execute a mailx command:

Apr 23 15:15:17 lnxopsd1as01 sendmail[8010]: o3NFFHwd008010: to=Marty.Johnson@staples.com, ctladdr=root (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30045, relay=[127.0.0.1] [127.0.0.1], dsn=4.0.0, stat=Deferred: Connection refused by [127.0.0.1]

Marty

Re: mailx port

Patrick Wallek — Fri, 23 Apr 2010 15:20:44 GMT

>>stat=Deferred: Connection refused by [127.0.0.1]

That is the key. The connection is refused. That was also the case with your 'telnet localhost 25'.

There are 2 possiblities:

1) There is nothing listening on port 25

2) Port 25 may be blocked by your firewall.

Re: mailx port

Martin Johnson — Fri, 23 Apr 2010 15:48:00 GMT

Patrick,

I suspect it is a firewall issue.
lsof -i:25 shows nothing is listening on port 25. It also shows nothing is listening on a node where I can send a successful mail message.

Marty

Re: mailx port

Martin Johnson — Fri, 23 Apr 2010 16:09:07 GMT

Actually, the problem turned out to be sendmail was not running. I started sendmail and received a bunch of messages. I guess the messages queue up when sendmail is not running.

Marty

Re: mailx port

Martin Johnson — Fri, 23 Apr 2010 16:12:25 GMT

See my last entry.

Re: mailx port

Steven Schweda — Fri, 23 Apr 2010 17:49:45 GMT

> telnet: Unable to connect to remote host: Connection refused

"Connection refused" normally means that you
could communicate with the server system, but
that no one is listening at the requested
port. That is, no server is registered with
inetd (or equivalent) for that port, or else
no inetd-independent server is running which
would listen at that port.

> [...] sendmail was not running.

Like that. It's possible, but relatively
rare, that a firewall will cause that
complaint. Normally, a firewall blockage
will look more like an immediate connection
failure, not a no-listener-at-this-port
problem.

Re: mailx port

Steven Schweda — Fri, 23 Apr 2010 17:58:02 GMT

By the way, ...

> [...] My problem is I don't know which port
> mailx uses, so I don't know which port to
> open.
>
> Ten points for the right answer!

> SMTP normally uses port 25.

That answer was exactly what you asked for.
It's not my fault that you were asking the
wrong question (or that you were so tardy in
running the suggested test).

> [...] I'm sure it is a firewall issue. [...]

> I suspect it is a firewall issue. [...]

Sometimes actual evidence can be more useful
than either groundless certainty or
suspicion.