I need to get a look at how my SSL mailserver plays with others; for non-SSL this is easy to do with (e.g.) telnet. Is there a bonified SSL/TLS client that can be used the same way?
Check SMTP over SSL
email;ssl;smtp
Yep, gnutls-cli, but there are a few minor tricks required to get it to work.gnutls-cli --crlf foobar.com -p 465Some online tutorials for this use -s foobar.com.  This does not seem to be necessary, although if the above fails you could try it.  If you use -s you will have to hit CtrlD (to send EOF) afterward in order to initiate the TLS session.--crlf is required because the (E)SMTP protocol uses a DOS style carriage return, line feed to end lines.  Without this the server will not respond.-p is for port, and here I've used the fairly standard 465 for SMTP over SSL.You should see some (copious) output regarding the server's certificate ending with:- Handshake was completed- Simple Client Mode:And hopefully right after that the first statement from the server:220 mailserver1.foobar.com ESMTPYou can now do whatever it was you were thinking of doing with telnet; since in this case it is ESMTP we use EHLO instead of HELOEHLO fake.orgThe server should reply with a list of characteristics/capabilities, or perhaps if very vigilant, say sorry, fake.org appears to be a lie ;)