67 lines
3.4 KiB
HTML
67 lines
3.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->
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<HTML>
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<HEAD>
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<TITLE>How is Mail Delivered?</TITLE>
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</HEAD>
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<BODY LANG="EN">
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<A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node189.html">Email Addresses</A>
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<B>Up:</B> <A HREF="node186.html">Electronic Mail</A>
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<B> Previous:</B> <A HREF="node187.html">What is a Mail </A>
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<BR> <P>
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<H1><A NAME="SECTION0015200000">How is Mail Delivered?</A></H1>
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<A NAME="maildelivery"></A>
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Generally, you will compose mail using a mailer interface like mail
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or mailx; or more sophisticated ones like elm, mush,
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or pine. These programs are called <em>mail user agents</em>, or MUA's
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for short. If you send a mail message, the interface program will in most
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cases hand it to another program for delivery. This is called the
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<em>mail transport agent</em>, or MTA. On some systems, there are different
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mail transport agents for local and remote delivery; on others, there is
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only one. The command for remote delivery is usually called rmail,
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the other is called lmail (if it exists).
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<P>
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Local delivery of mail is, of course, more than just appending the
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incoming message to the recipient's mailbox. Usually, the local MTA
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will understand aliasing (setting up local recipient addresses pointing
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to other addresses), and forwarding (redirecting a user's mail to some
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other destination). Also, messages that cannot be delivered must usually
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be <em>bounced</em>, that is, returned to the sender along with some
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error message.
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<P>
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For remote delivery, the transport software used depends on the nature
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of the link. If the mail must be delivered over a network using TCP/IP,
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SMTP is commonly used. SMTP stands for Simple Mail Transfer Protocol,
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and is defined in RFC-788 and RFC-821. SMTP usually connects to the
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recipient's machine directly, negotiating the message transfer with the
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remote side's SMTP daemon.
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<P>
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In UUCP networks, mail will usually not be delivered directly, but
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rather be forwarded to the destination host by a number of intermediate
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systems. To send a message over a UUCP link, the sending MTA will
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usually execute rmail on the forwarding system using uux,
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and feed it the message on standard input.
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<P>
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Since this is done for each message separately, it may produce a
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considerable work load on a major mail hub, as well as clutter the UUCP
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spool queues with hundreds of small files taking up an unproportional
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amount of disk space.<A HREF="footnode.html#6870"><IMG ALIGN=BOTTOM ALT="gif" SRC="foot_motif.gif"></A> Some MTAs therefore allow you to collect several messages for a remote
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system in a single batch file. The batch file contains the SMTP commands
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that the local host would normally issue if a direct SMTP connection was
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used. This is called BSMTP, or <em>batched</em> SMTP. The batch is then
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fed to the rsmtp or bsmtp program on the remote system,
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which will process the input as if a normal SMTP connection had
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occurred.
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<P>
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<HR><A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node189.html">Email Addresses</A>
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<B>Up:</B> <A HREF="node186.html">Electronic Mail</A>
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<B> Previous:</B> <A HREF="node187.html">What is a Mail </A>
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<P><ADDRESS>
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<I>Andrew Anderson <BR>
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Thu Mar 7 23:22:06 EST 1996</I>
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</ADDRESS>
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</BODY>
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</HTML>
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