I was just curious about the fact that openssl s_client -connect exchangeserver:993 was not working the way I expected it to work. I saw the greeting of the server but wasn’t able to do send any commands such as A1 CAPABILITY. The same worked for all other servers in the past.
Interestingly enough telnet exchangeserver 143 worked, but for obvious reasons unencrypted connections are not an option.
The reason behind is that in fact IMAP and telnet protocol and uses CRLF as line endings and Exchange servers are a bit picky on this specific point. As openssl is not a native client like telnet it sends whatever the terminal uses.
However there is already an solution builtin openssl s_client. Just pass the additional crlf option:
$ openssl s_client -connect exchangeserver:993 -crlf