In witness thereof I give you the following exchange between me and my mail server. I was doing a 'manual' connection (pointing telnet at port 25 -- the SMTP port number) to verify connectivity through the firewall. My commands are in bold, the mail server's responses are in italics.
beta:~$ telnet wixer.syrinx.org 25...If only some people could be that pleasent. :-)
Connected to wixer.syrinx.org.
Escape character is '^]'.
220 wixer.syrinx.org ESMTP Sendmail 8.12.11/8.12.11; Thu, 11 May 2006 09:13:54 -0400
250 wixer.syrinx.org Hello beta [126.96.36.199], pleased to meet you
221 2.0.0 wixer.syrinx.org closing connection
Connection closed by foreign host.