[698] in RedHat Linux List
Re: Sendmail Question
daemon@ATHENA.MIT.EDU (Steve \"Stevers!\" Coile)
Thu Oct 24 09:04:38 1996
Date: Thu, 24 Oct 1996 09:01:37 -0400 (EDT)
From: "Steve \"Stevers!\" Coile" <scoile@patriot.net>
To: Allen Francom <afrancom@numedics.transport.com>
cc: redhat-list@redhat.com
In-Reply-To: <Pine.LNX.3.91.961024092945.1557E-100000@numedics.transport.com>
Resent-From: redhat-list@redhat.com
Reply-To: redhat-list@redhat.com
On Thu, 24 Oct 1996, Allen Francom wrote:
> How it goes is like this...
>
> There's prorams that "run in the background" on Linux. Relative to mail,
> we have SENDMAIL, SMTP, POP2, POP3, and UUCP.
>
> Sendmail is a router, nothing more.
Sendmail is a lot of things, actually.
> SMTP is a "forwarding agent" - Is that a good description ?
> Simple Mail Transport Protocol
SMTP is a protocol, not a program. There is no program called "smtp"
on my 3.0.3 box, at least. Sendmail (among other programs) speaks SMTP.
> POP is Post Office Protocol.
POP is, indeed, a protocol. One might also speak of POP servers or
POP daemons. These are the programs that listen for and respond to
Post Office Protocol requests. POP clients are programs that make POP
requests of the POP servers.
>To make some analogies, sendmail is like the guy in the back room of
>the post office, sorting mail into this bin or that bin. SMTP is like
>the mail man, he picks up mail from the post office and delivers it to
>other mail-men, or other post-offices, he also can pick it up from the
>mail box and bring it back to the post office. POP is like a P.O. Box,
>you have to go to it to get your mail.
Actually, sendmail would be the postal service infrastructure.
Not only is sendmail the guy in the back of the post office sorting
the mail into different bins for delivery, he's also the guy driving
the truck carrying the mail to the next post office, and he's the guy
at the front desk taking incoming mail and providing customer service.
Sendmail is also responsible for forwarding your mail (as directed by your
".forward" file).
The equivalent of the mailman is the local mail delivery agent, which
under Red Hat Linux is procmail. Sendmail, after sorting the mail and
deciding who gets what, passes it off to procmail, who then finds the
appropriate mailbox and places the delivery in it. Some local mail
delivery agents are more sophisticated than others. Procmail is a very
sophisticated mailman, and can act on delivery instructions from the
recipient (provided via the ".procmailrc" file).
POP actually doesn't have an equivalent in the postal world. Using a POP
client is kinda like telling your kid to go get the mail from the mailbox.
At the point POP comes into play, your mail has already been delivered,
you just have to get it from the mailbox and read it. Relating POP to
post office boxes is probably appropriate, since POP is used to obtain
mail from a remote mailbox just as you would have to go the post office
to get your mail from a P.O. box.
UUCP, the UNIX-to-UNIX copy program (or protocol), is no longer in quite
as wide-spread use as it once was. UUCP might be equated to the company
employee that picks up the company's mail from the post office then
distributes it to the appropriate people back at the office. Typically,
UUCP was used to fetch all mail destined for a particular site from an
up-stream post office. After fetching, some mechanism would assist UUCP
in separating, sorting and delivering the mail to the users of the system.
> Does that help ?
>
> POP has no way to accept mail from a user and forward it to another. It
> retrieves mail only.
Depends on your perspective. POP is used to both deliver and retreive.
POP is a client/server protocol, and is used on the post office end
(by the POP server) and on the PC end (by the POP client). The two
ends communicate with each other using the protocol to pass mail from
the mailbox at the post office to the user on the PC.
-S
--
PLEASE read the Red Hat FAQ, Tips, HOWTO and the MAILING LIST ARCHIVES!
________________________________________________________________________
http://www.redhat.com/RedHat-FAQ http://www.redhat.com/RedHat-HOWTO
http://www.redhat.com/RedHat-Tips http://www.redhat.com/mailing-lists
------------------------------------------------------------------------
To unsubscribe: mail -s unsubscribe redhat-list-request@redhat.com < /dev/null
