My server had some issues sending mail in a secure manner. Somehow that SASL Authentication failed. After this was fixed I wanted to determine what TLS version and ciphers were used. After some time searching the web for an online tool that would do the job for me I thought about an OpenSSL parameter that could do the job for me. Run the following command:

openssl s_client -connect somedomain.tld:25 -starttls smtp

Of course it should represent the content of the MX record for that domain. In my case the following output was what I wanted to know:

New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES256-GCM-SHA384

Good luck!