Can't telnet localhost smtp

Question

I'm trying to use telnet (debian lenny 5.0.2) to check behavior of a postfix installation, but I can't telnet to smtp.

telnet localhost smtp
telnet: Unable to connect to remote host: Connection refused

telnetting to port 25 doesn't work either. I can telnet to port 110 and pop3.

How should I go about debugging this?

UPDATE: The command ps aux|grep 'postfix' revealed that postfix wasn't running. Inspection of /var/log/mail.err and /etc/postfix/main.cf uncovered a typo in main.cf. After correcting that, postfix ran fine.

Note that 'postfix start' returned a message reporting that postfix was starting. When postfix wasn't starting, no error message or warning was returned.

Answer 1

• First: check if Postfix is running: ps aux | grep postfix
• Second: check if somebody is actually listening on port 25: netstat -lnp | grep :25
• Third: if all of the above is ok, then probably the system firewall is preventing you from opening that sort of connection; have a look at its configuration using iptables -L.

Answer 2

For future searchers on this question, it is possible to have postfix (or any other server) running but specifically not listening on localhost. It can bind to individual addresses which are not localhost.

If netstat's output says anything but *.25 or 0.0.0.0:25, there is a good chance you've bound to whatever interface is running and you'll have to telnet to that IP (which is still local!)

In other words, localhost is not the same as the IP running on your machine.