An EHLO with Extensions
$ telnet/port=25 dbc.mtview.ca.us
Trying... Connected to DBC.MTVIEW.CA.US, a SUN-SPARC running UNIX.
220 dbc.mtview.ca.us SMTP server ready.
250-Hello , pleased to meet you
221 dbc.mtview.ca.us closing connection
Connection closed by Foreign Host
A mailer that supports extensions responds with a list of which ones it can do