SSL is being used more often than plain text connections, so the usual testing with telnet may not work anymore.
Fortunately, it's possible to use openssl command to test webservers, POP3S/IMAPS/SMTPS mailserver, FTPS servers etc. which use SSL.
Testing HTTPS
Testing SSMTP / SMTPS
Or, to test TLS on port 25:
Testing IMAP on port 143
Note the "-starttls imap" added to the command line - this one shows an expired certificate:
