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<LI><A NAME="tex2html1918"
  HREF="#SECTION001310000000000000000">10.1 Sending and Reading Mail</A>
<LI><A NAME="tex2html1919"
  HREF="#SECTION001320000000000000000">10.2 The SMTP Protocol -- Sending Mail Raw to Port <TT>
<FONT COLOR="#0000ff">25</FONT></TT></A>
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<H1><A NAME="SECTION001300000000000000000">
10. Mail</A>
</H1>

<P>
<A NAME="chap:mailclient"></A>
<P>
<I>Electronic Mail</I>, or <I>e</I>mail, is the way most people first come into
contact with the Internet. Although you may have used email in a graphical environment,
here we show you how mail was first intended to be used on a multiuser system.
To a large extent what applies here is really what is going on in the
background of any system that supports mail.

<P>
A mail message is a block of text sent from one user to another,
using some mail command or mailer program. A mail
message will usually also be accompanied by a <I>subject</I>
explaining what the mail is about. The idea of mail is that a
message can be sent to someone even though he may not be logged
in at the time and the mail will be stored for him until he is
around to read it. An email address is probably familiar to you,
for example: <TT>
<FONT COLOR="#0000ff">bruce@kangeroo.co.au</FONT></TT>. This means that
<TT>
<FONT COLOR="#0000ff">bruce</FONT></TT> has a user account on a computer called
<TT>
<FONT COLOR="#0000ff">kangeroo.co.au</FONT></TT>, which often means that he can log in as
<TT>
<FONT COLOR="#0000ff">bruce</FONT></TT> on that machine. The text after the <TT>
<FONT COLOR="#0000ff">@</FONT></TT> is always
the name of the machine. Today's Internet does not obey this
exactly, but there is always a machine that <TT>
<FONT COLOR="#0000ff">bruce</FONT></TT>
<I>does</I> have an account on where mail is eventually sent.
 <FONT COLOR="#ffa500">[That machine is also usually a U<SMALL>NIX</SMALL> machine.]</FONT>
<P>
Sometimes email addresses are written in a more user-friendly
form like <TT>
<FONT COLOR="#0000ff">Bruce Wallaby &#60;bruce@kangeroo.co.au&#62;</FONT></TT> or
<TT>
<FONT COLOR="#0000ff">bruce@kangeroo.co.au (Bruce Wallaby)</FONT></TT>. In this case,
the surrounding characters are purely cosmetic;
only <TT>
<FONT COLOR="#0000ff">bruce@kangeroo.co.au</FONT></TT> is ever used.

<P>
When mail is received for you (from another user on the system or from a
user from another system) it is appended to the file <TT>
<FONT COLOR="#0000ff">/var/spool/mail/&lt;username&gt;</FONT></TT>
called the <I>mail file</I> or <I>mailbox file</I>;
<TT>
<FONT COLOR="#0000ff">&lt;username&gt;</FONT></TT> is your login name. You then run some program that interprets your mail file, allowing
you to browse the file as a sequence of mail messages and read and reply to
them.

<P>
An actual addition to your mail file might look like this:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red size="-1">
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>5</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>10</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>15</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>20</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>25</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>30</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>35</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue size="-1">
<code>From&nbsp;mands@inetafrica.com&nbsp;&nbsp;Mon&nbsp;Jun&nbsp;&nbsp;1&nbsp;21:20:21&nbsp;1998</code><br>
<code>Return-Path:&nbsp;&#060;mands@inetafrica.com&#062;</code><br>
<code>Received:&nbsp;from&nbsp;pizza.cranzgot.co.za&nbsp;(root@pizza.cranzgot.co.za&nbsp;[192.168.2.254])</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;by&nbsp;onion.cranzgot.co.za&nbsp;(8.8.7/8.8.7)&nbsp;with&nbsp;ESMTP&nbsp;id&nbsp;VAA11942</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;&#060;psheer@cranzgot.co.za&#062;&#059;&nbsp;Mon,&nbsp;1&nbsp;Jun&nbsp;1998&nbsp;21:20:20&nbsp;+0200</code><br>
<code>Received:&nbsp;from&nbsp;mail450.icon.co.za&nbsp;(mail450.icon.co.za&nbsp;[196.26.208.3])</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;by&nbsp;pizza.cranzgot.co.za&nbsp;(8.8.5/8.8.5)&nbsp;with&nbsp;ESMTP&nbsp;id&nbsp;VAA19357</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;&#060;psheer@cranzgot.co.za&#062;&#059;&nbsp;Mon,&nbsp;1&nbsp;Jun&nbsp;1998&nbsp;21:17:06&nbsp;+0200</code><br>
<code>Received:&nbsp;from&nbsp;smtp02.inetafrica.com&nbsp;(smtp02.inetafrica.com&nbsp;[196.7.0.140])</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;by&nbsp;mail450.icon.co.za&nbsp;(8.8.8/8.8.8)&nbsp;with&nbsp;SMTP&nbsp;id&nbsp;VAA02315</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;&#060;psheer@cranzgot.co.za&#062;&#059;&nbsp;Mon,&nbsp;1&nbsp;Jun&nbsp;1998&nbsp;21:24:21&nbsp;+0200&nbsp;(GMT)</code><br>
<code>Received:&nbsp;from&nbsp;default&nbsp;[196.31.19.216]&nbsp;(fullmoon)</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;by&nbsp;smtp02.inetafrica.com&nbsp;with&nbsp;smtp&nbsp;(Exim&nbsp;1.73&nbsp;#1)</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;id&nbsp;0ygTDL-00041u-00&#059;&nbsp;Mon,&nbsp;1&nbsp;Jun&nbsp;1998&nbsp;13:57:20&nbsp;+0200</code><br>
<code>Message-ID:&nbsp;&#060;357296DF.60A3@inetafrica.com&#062;</code><br>
<code>Date:&nbsp;Mon,&nbsp;01&nbsp;Jun&nbsp;1998&nbsp;13:56:15&nbsp;+0200</code><br>
<code>From:&nbsp;a&nbsp;person&nbsp;&#060;mands@inetafrica.com&#062;</code><br>
<code>Reply-To:&nbsp;mands@inetafrica.com</code><br>
<code>Organization:&nbsp;private</code><br>
<code>X-Mailer:&nbsp;Mozilla&nbsp;3.01&nbsp;(Win95&#059;&nbsp;I)</code><br>
<code>MIME-Version:&nbsp;1.0</code><br>
<code>To:&nbsp;paul&nbsp;sheer&nbsp;&#060;psheer@cranzgot.co.za&#062;</code><br>
<code>Subject:&nbsp;hello</code><br>
<code>Content-Type:&nbsp;text/plain&#059;&nbsp;charset=us-ascii</code><br>
<code>Content-Transfer-Encoding:&nbsp;7bit</code><br>
<code>Status:&nbsp;RO</code><br>
<code>X-Status:&nbsp;A</code><br>
<code>&nbsp;</code><br>
<code>hey&nbsp;paul</code><br>
<code>its&nbsp;me</code><br>
<code>how&nbsp;r&nbsp;u&nbsp;doing</code><br>
<code>i&nbsp;am&nbsp;well</code><br>
<code>what&nbsp;u&nbsp;been&nbsp;upot</code><br>
<code>hows&nbsp;life</code><br>
<code>hope&nbsp;your&nbsp;well</code><br>
<code>amanda</code><br>
</FONT></TD></TR></TABLE><P>

<P>
Each mail message begins with a <TT>
<FONT COLOR="#0000ff">From</FONT></TT> at the beginning
of a line, followed by a space. Then comes the <I>mail header</I>,
explaining where the message was routed from to get
to your mailbox, who sent the message, where replies should
go, the subject of the mail, and various other <I>mail header fields</I>. Above,
the header is longer than the mail messages. Examine the header
carefully.

<P>
The header ends with the first blank line. The message itself
(or <I>body</I>) starts right after. The next header in the file
will once again start with a <TT>
<FONT COLOR="#0000ff">From</FONT></TT>. <TT>
<FONT COLOR="#0000ff">From</FONT></TT>s on
the beginning of a line <I>never</I> exist within the body.
If they do, the mailbox is considered to be corrupt.

<P>
Some mail readers store their messages in a different format.
However the above format (called the <I>mbox</I> format) is the
most common for U<SMALL>NIX</SMALL>. Of interest is a format called <I>Maildir</I>,
which is one format that does <I>not</I> store mail messages
in a single contiguous file. Instead, <I>Maildir</I> stores each message
as a separate file within a directory. The name of the directory is
then considered to be the mailbox ``file''; by default Maildir uses a
directory <TT>
<FONT COLOR="#0000ff">Maildir</FONT></TT> within the user's home directory.

<P>

<H1><A NAME="SECTION001310000000000000000">
10.1 Sending and Reading Mail</A>
</H1>

<P>
The simplest way to send mail is to use the <TT>
<FONT COLOR="#0000ff">mail</FONT></TT> command.
Type <TT>
<FONT COLOR="#0000ff">mail
-s&nbsp;&#34;hello&nbsp;there&#34;&nbsp;&lt;username&gt;</FONT></TT>. The <TT>
<FONT COLOR="#0000ff">mail</FONT></TT>
program will then wait for you to type out your message. When you are
finished, enter a <TT>
<FONT COLOR="#0000ff">.</FONT></TT> on its own on a single line. The
user name will be another user on your system. If no one else is
on your system, then send mail to <TT>
<FONT COLOR="#0000ff">root</FONT></TT> with
<TT>
<FONT COLOR="#0000ff">mail -s "Hello there" root</FONT></TT> or <TT>
<FONT COLOR="#0000ff">mail -s "Hello there" root@localhost</FONT></TT> (if
the @ is not present, then the local machine, <TT>
<FONT COLOR="#0000ff">localhost</FONT></TT>, is implied).
Sending files over email is discussed in Section <A HREF="node15.html#sec:filesoveremail">12.6</A>.

<P>
You can use <TT>
<FONT COLOR="#0000ff">mail</FONT></TT> to view your mailbox. This is a
primitive utility in comparison with modern graphical mail readers
but is probably the only mail reader that can handle arbitrarily
sized mailboxes. Sometimes you may get a mailbox that is over a
gigabyte in size, and <TT>
<FONT COLOR="#0000ff">mail</FONT></TT> is the only way to delete
messages from it. To view your mailbox, type <TT>
<FONT COLOR="#0000ff">mail</FONT></TT>, and then
<TT>
<FONT COLOR="#0000ff">z</FONT></TT> to read your next window of messages, and <TT>
<FONT COLOR="#0000ff">z-</FONT></TT> to view
the previous window. Most commands work like <I>command</I>
<I>message_number</I>, for example, <TT>
<FONT COLOR="#0000ff">delete 14</FONT></TT> or <TT>
<FONT COLOR="#0000ff">reply 7</FONT></TT>.
The message number is the left column with an <TT>
<FONT COLOR="#0000ff">N</FONT></TT> next to it (for a
<TT>
<FONT COLOR="#0000ff">N</FONT></TT>ew message).

<P>
For the state of the art in terminal-based mail readers (also called
mail <I>clients</I>), try
<TT>
<FONT COLOR="#0000ff">mutt</FONT></TT> and <TT>
<FONT COLOR="#0000ff">pine</FONT></TT>. <FONT COLOR="#ffa500">[<TT>
<FONT COLOR="#0000ff">pine</FONT></TT>'s license is not Free.]</FONT>
<P>
There are also some graphical mail readers in various stages of
development. At the time I am writing this, I have been using
<TT>
<FONT COLOR="#0000ff">balsa</FONT></TT> for a few months, which was the best mail reader
I could find.

<P>

<H1><A NAME="SECTION001320000000000000000">
10.2 The SMTP Protocol -- Sending Mail Raw to Port <TT>
<FONT COLOR="#0000ff">25</FONT></TT></A>
</H1>

<P>
<A NAME="sec:sendamail"></A>
<P>
To send mail, you need not use a mail client at all. The mail
client just follows <I>SMTP</I> (Simple Mail Transfer Protocol), which you can type in from the keyboard.

<P>
For example, you can send mail by <TT>
<FONT COLOR="#0000ff">telnet</FONT></TT><I>ing</I> to
<I>port 25</I> of a machine that has an
<I>MTA</I> (Mail Transfer Agent--also called the <I>mailer daemon</I>
or <I>mail server</I>)
running. The word <I>daemon</I> denotes programs that
run silently without user intervention.

<P>
<A NAME="sec:spam"></A>This is, in fact, how so-called <I>anonymous mail</I> or
<I>spam mail</I> <FONT COLOR="#ffa500">[<I>Spam</I> is a term used to indicate
unsolicited email--that is, junk mail that is posted in bulk to
large numbers of arbitrary email addresses. Sending spam is considered
unethical Internet practice.]</FONT> is sent on the Internet. A mailer
daemon runs in most small institutions in the world and has the
simple task of receiving mail requests and relaying them on to other
mail servers. Try this, for example (obviously substituting
<TT>
<FONT COLOR="#0000ff">mail.cranzgot.co.za</FONT></TT> for the name of a mail server that you
normally use):

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red size="-1">
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>5</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>10</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>15</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>20</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue size="-1">
<code>[root@cericon]#&nbsp;<font color="navy"><B>telnet&nbsp;mail.cranzgot.co.za&nbsp;25</B></font></code><br>
<code>Trying&nbsp;192.168.2.1...</code><br>
<code>Connected&nbsp;to&nbsp;192.168.2.1.</code><br>
<code>Escape&nbsp;character&nbsp;is&nbsp;'^]'.</code><br>
<code>220&nbsp;onion.cranzgot.co.za&nbsp;ESMTP&nbsp;Sendmail&nbsp;8.9.3/8.9.3&#059;&nbsp;Wed,&nbsp;2&nbsp;Feb&nbsp;2000&nbsp;14:54:47&nbsp;+0200</code><br>
<code><font color="navy"><B>HELO&nbsp;cericon.cranzgot.co.za</B></font></code><br>
<code>250&nbsp;onion.cranzgot.co.za&nbsp;Hello&nbsp;cericon.ctn.cranzgot.co.za&nbsp;[192.168.3.9],&nbsp;pleased&nbsp;to&nbsp;meet&nbsp;yo</code><br>
<code><font color="navy"><B>MAIL&nbsp;FROM:psheer@cranzgot.co.za</B></font></code><br>
<code>250&nbsp;psheer@cranzgot.co.za...&nbsp;Sender&nbsp;ok</code><br>
<code><font color="navy"><B>RCPT&nbsp;TO:mands@inetafrica.com</B></font></code><br>
<code>250&nbsp;mands@inetafrica.com...&nbsp;Recipient&nbsp;ok</code><br>
<code><font color="navy"><B>DATA</B></font></code><br>
<code>354&nbsp;Enter&nbsp;mail,&nbsp;end&nbsp;with&nbsp;"."&nbsp;on&nbsp;a&nbsp;line&nbsp;by&nbsp;itself</code><br>
<code><font color="navy"><B>Subject:&nbsp;just&nbsp;to&nbsp;say&nbsp;hi</B></font></code><br>
<code>&nbsp;</code><br>
<code><font color="navy"><B>hi&nbsp;there</B></font></code><br>
<code><font color="navy"><B>heres&nbsp;a&nbsp;short&nbsp;message</B></font></code><br>
<code>&nbsp;</code><br>
<code><font color="navy"><B>.</B></font></code><br>
<code>250&nbsp;OAA04620&nbsp;Message&nbsp;accepted&nbsp;for&nbsp;delivery</code><br>
<code><font color="navy"><B>QUIT</B></font></code><br>
<code>221&nbsp;onion.cranzgot.co.za&nbsp;closing&nbsp;connection</code><br>
<code>Connection&nbsp;closed&nbsp;by&nbsp;foreign&nbsp;host.</code><br>
<code>[root@cericon]#&nbsp;</code><br>
</FONT></TD></TR></TABLE><P>

<P>
The above causes the message ``<TT>
<FONT COLOR="#0000ff">hi there heres a short
message</FONT></TT>'' to be delivered to <TT>
<FONT COLOR="#0000ff">mands@inetafrica.com</FONT></TT> (the
<TT>
<FONT COLOR="#0000ff">R</FONT></TT><I>e</I><TT>
<FONT COLOR="#0000ff">C</FONT></TT><I>i</I><TT>
<FONT COLOR="#0000ff">P</FONT></TT><I>ien</I><TT>
<FONT COLOR="#0000ff">T</FONT></TT>).
Of course, I can enter any address that I like as the sender, and it
can be difficult to determine who sent the message. In this
example, the <TT>
<FONT COLOR="#0000ff">Subject:</FONT></TT> is the only header field, although
I needn't have supplied a header at all.

<P>
Now, you may have tried this and gotten a rude error message. This
might be because the MTA is configured <I>not</I> to relay mail
except from specific trusted machines--say, only those
machines within that organization. In this way anonymous email is prevented.

<P>
On the other hand, if you are connecting to the user's very own mail
server, it has to necessarily receive the mail, regardless of who sent it. Hence, the above is a
useful way to supply a bogus <TT>
<FONT COLOR="#0000ff">FROM</FONT></TT> address and thereby
send mail almost anonymously. By ``almost'' I mean that the mail
server would still have logged the machine from which you
connected and the time of connection--there is no perfect anonymity
for properly configured mail servers.

<P>
The above technique is often the only way to properly test a mail
server, and should be practiced for later.

<P>
<HR>
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