Problem with incoming mail

I have a hosted web server running FC3 and Plesk. Incoming mail has
stopped and messages sent externally to addresses on the server are
getting reports of delivery delays along the line of the server not
accepting connections. I have been making various updates to
..procmailrc files but can't think of anything I have done which would
have had this effect. I have reported it to the hosting company and
they are investigating. Given that I know very little about mail and
how it moves through the server I wondered if there was anything I
could do to investigate it myself, maybe fixing it before they do. I
would like to know more of what goes on in the process so this seems
like a good learning exercise.

As far as I know the server uses procmail, qmail and courier. I don't
know what role these play, can someone suggest what I can do to
investigate how it works and what might be broken? I have root access
so should be in a position to do / check most things.

Hopefully I can learn how the thing actually works if not actually fix
it before they do.

Any suggestions on where to start?

Thanks,
Geoff

PS please reply on usenet due to my e-mail problems!!

Re: Problem with incoming mail

Geoff Soper wrote:
> I have a hosted web server running FC3 and Plesk. Incoming mail has
> stopped and messages sent externally to addresses on the server are
> getting reports of delivery delays along the line of the server not
> accepting connections. I have been making various updates to
> .procmailrc files but can't think of anything I have done which would
> have had this effect. I have reported it to the hosting company and
> they are investigating. Given that I know very little about mail and
> how it moves through the server I wondered if there was anything I
> could do to investigate it myself, maybe fixing it before they do. I
> would like to know more of what goes on in the process so this seems
> like a good learning exercise.
>
> As far as I know the server uses procmail, qmail and courier. I don't
> know what role these play, can someone suggest what I can do to
> investigate how it works and what might be broken? I have root access
> so should be in a position to do / check most things.
>
> Hopefully I can learn how the thing actually works if not actually fix
> it before they do.
>
> Any suggestions on where to start?
>
> Thanks,
> Geoff
>
> PS please reply on usenet due to my e-mail problems!!

Another way of asking this might be to ask how mail works on a server.
I think I know some pieces of the jigsaw:

- DNS specifies one or more mail servers for a domain i.e.
mail.domain.tld
- Other mail servers use this/these addresses and contact them on a
port, 25? SMTP?
- Something on the server listens on this port and accepts mails. Is
this what might be broken and what software would likely carry out this
job?
- Something on the server delivers the mail to the correct mail
directory. Qmail with help from Procmail?
- Courier then serves IMAP/POP3 to clients, something like Apache might
serve HTTP(S)?

Am I on the right track?

Cheers,
Geoff