??? Withpipelining, SMTP
commands and replies do not have to be synchronized. To illustrate, consider the following
example of a normal (not pipelined) SMTP dialog, in which the server machine??™s half of the
dialog is shown in bold font and the client machine??™s dialog is not:
220 your.host ESMTP Sendmail 8.14.1/8.14.1; Thu, 14 Dec 2007 08:12:44 -0700 (MST)
HELO some.domain.com
250 your.host.domain Hello some.domain.com [123.45.67.8], pleased to meet you
* Eric was getting complaints that the continual insertion of this warning was misleading and tended to cause
people to ignore it entirely.
This is the Title of the Book, eMatter Edition
Copyright ?© 2007 O??™Reilly & Associates, Inc. All rights reserved.
134 | Chapter 3: Tune sendmail with Compile-Time Macros
MAIL FROM:
250 2.1.0 ... Sender ok
RCPT TO:
250 2.1.5 ... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
?†? message sent, end with a dot
.
250 2.0.0 g1GFCigc025138 Message accepted for delivery
QUIT
221 2.0.0 your.host closing connection
The important point to notice about this SMTP conversation is that it is synchronous. The
client machine always waits for a reply from the server before sending its next command.
For example, in the preceding dialog it waits for the 220 before sending the HELO command,
and then waits for the 250 before sending the MAIL command.
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