openssl s_client -starttls smtp -showcerts -connect XX.X.XX.X:25 -servername mail.example.com
CONNECTED(00000004)
Didn't find STARTTLS in server response, trying anyway...
write:errno=0
---
no peer certificate available
---
No client certificate CA names sent
---
SSL handshake has read 51 bytes and written 351 bytes
Verification: OK
---
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)
---
$