Re: Emacs Manual: Mail sending via SMTP

[Alex Schroeder <alex@emacswiki.org>]

Simon Josefsson <jas@extundo.com> writes:

> Since it is now a standalone manual, I think everything that we can
> say about the library is appropriate.

Yay!  Maybe we can expand it a bit more?  :)

Russel's answer to my original intro-paragraph made it clear that a
separate section might be appropriate -- explain MTA, MUA, SMTP (we
have these three already), POP3, IMAP (the two major players only),
spool, procmail (mail delivery agent, MDA?).

Here is an expanded version.

Cheers,

Alex "Document Mode" Schroeder.  :)




How Mail Works

   On the Internet, mail is sent from mail host to mail host using the
simple mail transfer protocol (SMTP).  To send and receive mail, you
must get it from and send it to a mail host.  Every mail host runs a
mail transger agent (MTA) such as sendmail that accepts mails and
passes them on.  The communication between a mail host and other
clients does not necessarily involve SMTP, however.  Here is short
overview of what is involved.

   The mail program -- also called a mail user agent (MUA) -- usually
sends outgoing mail to a mail host.  When your computer is permanently
connected to the internet, it might even be a mail host itself.  In
this case, the MUA will send mail to the SMTP port on the same
computer.  A local mail transfer agent (MTA) such as exim or sendmail
will take care of your mail and pass it on to the next mail host.

   When you are only connected to the internet from time to time, your
internet service provider (ISP) has probably told you which mail host
to use.  You must configure your MUA to use that mail host.  Since you
are reading this manual, you probably want to configure Emacs to use
SMTP to send mail to that mail host.  More on that in the next
section.

   Things are different when reading mail.  The mail host responsible
for your mail keeps it in a file somewhere.  When your computer is
that mail host, this file is called a spool, and sometimes located in
the directory /var/spool/mail/.  All your MUA has to do is read mail
from the spool, then.

   When your computer is not always connected to the Internet, you
must get the mail from the remote mail host using a protocol such as
POP3 or IMAP.  POP3 essentially downloads all your mail from the mail
host to your computer.  The mail is stored in some file on your
computer, and again, all your MUA has to do is read mail from the
spool.  Sometimes mail is passed to yet another program, a mail
delivery agent (MDA) such as procmail.  These delivery agents often
allow you to filter and munge your mails before you get to see it.

   When you read mail from various machines, downloading mail from the
mail host to your current machine is not convenient.  In that case,
you will probably want to use the IMAP protocol.  Your mail is kept on
the mail host, and you can read it while you are connected via IMAP to
the mail host.

   So how does reading mail via the web work, you ask.  In that case,
the web interface just allows you to remote-control a MUA on the web
host.  Whether the web host is also a mail host, and how all the
pieces interact is completely irrelevant.  You usually cannot use
Emacs to read mail via the web, unless you use software that parses
the ever-changing HTML of the web interface.

Emacs speaks SMTP 

   Emacs includes a package for sending your mail to a SMTP server and
have it take care of delivering it to the final destination, rather
than letting the MTA on your local system take care of it.  ...