S: 220 mail.example.net ESMTP
 C: EHLO mail.example.org
 S: 250-mail.example.net Hello example.org [192.0.2.1]
 S: 250-SIZE 52428800
 S: 250-8BITMIME
 S: 250-PIPELINING
 S: 250-STARTTLS
 S: 250 HELP
 C: STARTTLS
 S: TLS go ahead