[Gllug] Email servers

[Bruce Richardson]

On Tue, Feb 05, 2002 at 11:03:13PM +0000, Dylan wrote:
> Hi guys,
> 
> I've been trawling thru books and docs for days over this and have got 
> thoroughly confused. I want to set up the necessafy services so that one of 
> my machines will periodically collect mail (by POP3) from my ISP and then 
> allow it to be collected (again by POP3) by users' mail clients. I figure I 
> use fetchmail for doing the ISP collection, triggered by cron, but I don't 
> understand the stuff about maildrops and forwarding etc.

In this scenario, fetchmail would get the mail from the ISP pop server
and hand it to the MTA (sendmail, postfix, whatever).  The handover is
in the form of a standard SMTP exchange, as if fetchmail were a remote
mailserver delivering mail directly to you.

The MTA then has to decide what to do with it.  Classic Unix MTAs do not
store mail, they deliver it.  So the MTA has to either forward the mail
to another mailhost or deliver it to a local mailstore.  For this it
uses a local delivery agent (an external app like procmail or maybe an
internal process), which usually adds the mail to a local user's
mail-spool (by concatenating it to the end of a text file or placing it
as a series of text files in a directory).  The mailspool may be in a
location like /var/mail or /var/spool/mail or may be in a local user's
home directory.  Note: by local user I mean user account on the
mailhost, not local network user.

Now, when one of your network users wants to collect their mail, they
connect to the pop server, give a name and password and the daemon
fetches the mail from wherever local mailspools are stored - even if
that *is* some home directory somewhere.  The user downloads the mail to
their computer (possibly even by the same fetchmail/mta process that
fetched it from the ISP) and is happy.

> I don't want the 
> mail to end up in a users' home directory, I want them to be able to POP it 
> off the local network.

I hope the above explanation reassures you.  I know it can be confusing:
confused me at first.  When I was new to Linux, I networked a windows
box and my shiny new Linux box together and installed a simple pop
daemon on Linux.  When I tried to use Outlook to fetch my mail from the
Linux box I was surprised to see that the pop daemon grabbed all my mail
from /var/spool/mail/bruce and put it in /home/bruce/mbox before serving
it up to Outlook.

-- 
Bruce

You can fool some of the people all the time, you can fool all of
the people some of the time but you can never fool your mother.
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