Testing SSL certificates on remote server
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Testing your SSL certificates
From time to time I need to verify the SSL certificate configured for a server - either within the webserver or the mailserver. Here are a few commands I regularly use on a Linux host to verify the configuration on the remote server to test:
(replace HOST with either the hostname or an IP address)
Testing on a webserver
This is probably one of the most used commands when working on this topic:
openssl s_client -showcerts -connect HOST:443
Testing on a Mailserver (SMTP Submission)
The following tests the Submission Port (587), see the last parameter that initiates an SMTP session with the server:
openssl s_client -showcerts -connect HOST:587 -starttls smtp
Depending on the configuration of the mailserver, also port 25 contain an SSL certificate:
openssl s_client -showcerts -connect HOST:25 -starttls smtp
Testing on a Mailserver (IMAP)
The following tests the SSL certificate configured for encrypted IMAP on Port 993:
openssl s_client -showcerts -connect HOST:993
Testing on a Mailserver (POP3)
The following tests the SSL certificate configured for the POP3 server on port 995:
openssl s_client -showcerts -connect HOST:995