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Unformatted text preview: ons to SMTP.
The result is called extended SMTP (ESMTP). As with other new features that we've
described in the text, these changes are being added in a backward compatible manner, so
that existing implementations aren't affected.
A client that wishes to use the new features initiates the session with the server by issuing
a EHLO command, instead of HELO. A compatible server responds with a 250 reply file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/smtp_sim.htm (14 of 23) [12/09/2001 14.47.52] Chapter 28. SMTP: Simple Mail Transfer Protocol code. This reply is normally multiline, with each line containing a keyword and an
optional argument. These keywords specify the SMTP extensions supported by the server.
New extensions will be described in an RFC and will be registered with the IANA. (In a
multiline reply all lines except the last have a hyphen after the numeric reply code. The
last line has a space after the numeric reply code.)
We'll show the initial connection to four SMTP servers, three of which support extended
SMTP. We connect to them using Telnet, but have removed the extraneous Telnet client
sun % telnet vangogh.cs.berkeley.edu 25
220-vangogh.CS.Berkeley.EDU Sendmail 8.1C/6.32 ready at Mon,
2 Aug 1993 15: 47:48 -0700
220 ESMTP spoken here
250-vangogh.CS.Berkeley.EDU Hello sun.tuc.noao.edu
[184.108.40.206], pleased to meet you
This server gives a multiline 220 reply for its greeting message. The extended commands
listed in the 250 reply to the EHLO command are EXPN, SIZE, and HELP The first and
last are from the original RFC 821 specification, but they are optional commands. ESMTP
servers state which of the optional RFC 821 commands they support, in addition to newer
The SIZE keyword that this server supports is defined in RFC 1427 [Klensin, Freed, and
Moore 1993]. It lets the client specify the size of the message in bytes on the MAIL
FROM command line. This lets the server verify that it will accept a message of that size,
before the client...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12