Linux Networking Cookbook

19.15. Troubleshooting a POP3, POP3s, or IMAP Server

Problem

What are some tests you can run directly on your POP3, POP3s, or IMAP server to see if it is working correctly? You want to eliminate as many variables as you can and talk directly to the server, if that's possible.

Solution

telnet and Netstat will do the job for you. Netstat shows you if it is running and listening to the correct ports and addresses, as this example shows for Dovecot:

	# netstat -plunt | grep :110
	tcp   0   0 :::110 :::*      LISTEN    4654/dovecot

This shows that Dovecot is open to all connections, so if you want to limit it to LAN connections, you'll need to fix its configuration. Then, Netstat will report this:

	tcp  0  0 192.168.1.25:110 :::*   LISTEN   4654/dovecot

POP3s, which is POP3 over SSL, runs on TCP port 995.

IMAP runs on TCP port 143, and IMAP over SSL uses TCP port 993.

To test a POP3 server with telnet, you need to have a user account already set up on the server. Then, do this:

	$ telnet localhost 110
	Trying 127.0.0.1...
	Connected to localhost.localdomain.
	Escape character is '^]'.
	+OK Hello there.
	user carla
	+OK Password required.
	pass password
	+OK logged in.
	stat
	+OK 2 1275
	list
	+OK
	1 748
	2 1028
	3 922
	.

This shows a successful login, and the list command shows there are three messages. At this point, you can quit, or enter retr 1, retr 2, or retr 3 to read your messages. quit closes the session.

Use the s_client command, which is part of OpenSSL, to test POP3s:

	$ openssl s_client -connect localhost:995

This should ...