Testing Linux Mail Servers with OpenSSL

“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.

Complete
Story