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Testing Linux Mail Servers with OpenSSL

Feb 15, 2011, 21:34 (0 Talkback[s])
(Other stories by Carla Schroder)

"Yesterday Juliet Kemp showed us how to perform basic server tests with telnet. Today Carla Schroder shows how to test TLS/SSL-enabled POP3 and IMAP servers.

"This is a followup to Juliet Kemp's excellent Troubleshooting Linux Servers with telnet article. This is adapted from my aging but still-excellent Linux Cookbook.

"Testing POP3 TLS/SSL

"Telnet does not support any encryption. If you are protecting your POP3 sessions with TLS/SSL then you need s_client, which is part of OpenSSL. You can query both local and remote mail servers, using your own server names of course. Commands that you type are in bold:

$ openssl s_client -connect localhost.com:995
$ openssl s_client -connect remotehost.com:995

"You'll see a whole lot of lines about certificates and protocols, and eventually something like this:

+OK Dovecot ready.

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