----- Original Message -----
From: "John R. Shearer" <exim-users@???>
> > From what I gather then, it would not be possible for 2 mail servers to
> > contain a different list of addresses (MX records?) while considering
the
> > same domain as local.
>
> Uh, I have no idea what you just said. Maybe I can explain it anyway...
>
> 1. A given Exim mail server has a list of domains which it has mailboxes
in
> /var/mail for. These are "local_domains".
Yes - these were what were causing some pgi.com emails to appear in the
mainlog as being delivered.
Someone probably thought they were doing someone a favour by setting up
those several email addresses.
Is all that is necessary for exim to see an address as 'known' is that it
has an entry in /var/mail ?
> 2a. If the mail server receives a message, and the recipient's domain is
in
> local_domains, then the message [normally] gets written to
> /var/mail/username. Only directors get processed; routers are not.
And directors are rules by which email gets ... directed?
Directors and routers are similar constructs for different events?
(local vs. external delivery respectively)
> 2b. If the mail server receives a message, and the recipient's domain is
> *NOT* in local_domains, then the mail server will try to deliver it to a
> remote host. How? By asking the DNS for an MX record for the domain.
Ok - MX records confuse me slightly. Are MX records stored alongside the
DNS entry at the DNS server?
> > Or, more correctly, even if that was the case, only
> > one DNS entry would be returned to any MTA trying to deliver mail to
that
> > domain and that DNS entry would be linked to a single server and list of
> > addresses.
>
> This part makes sense, I think. In the case of 2b above the mail server
> will ask the DNS for all MX records associated with the domain. Hopefully
> it will get one (or more) back and, as I think you were eluding to above,
> that MX record will point to one (or more) A record(s), which in turn
point
> to one (or more) IP address(es).
I know this is elementary to dealing with internet mail, however I should
wrap my head around it sooner or later. What is the function of an MX
record as opposed to an A record?
My guess:
An MX record contains a list of addresses valid for a
particular domain. Each MX record then points to an A
record which contians more specific information about the
domain and a particular address.
This way, an MTA first can see if a domain even accepts mail
(it gets an MX record), second it can see if the address is
valid for that domain (entry within the MX record) and then
it can request an A record for directions on where and how
to deliver the actual message.
> The mail servers which those A records point to *might* consider the
domain
> in question to be local. They might also just forward the Email along to
> another host which really does consider it to be local.
So an A record doesn't necessarily define the end point of a message. Exim
can often forward email addresses along a chain of servers until a server
considers the address local - at which point it may get written to /var/mail
where a mail viewer can download it.
> Yes, it's complicated. I hope this helps explain it a little. :-)
I think I am getting it. I don't need to be a mail guru (ever), but a
cursory understanding of the process and technologies behind a program often
allow me to use it better.
Thank you _very_ much for your experience and time.
James.
