Use telnet to login to the server:
telnet localhost 25
After executing the following command:
ehlo localhost
you should get a response like this:
250-server1.example.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH PLAIN LOGIN
250-AUTH=PLAIN LOGIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
The following lines must be present:
250-STARTTLS
250-AUTH PLAIN LOGIN