Robert Cates wrote:
> Hi,
>
> I tried to write the author of this article, but it didn't work, so I
> thought I'd ask this list my question -
> http://author.handalak.com/archives/052006/000988
>
> His article nicely explains how to configure Virtual Domains in Exim
> 4.51, however, simply configuring Exim as he describes, does not allow
> friends (people in the outside world) to send mail to any Virtual Domain
> in Exim. Those Virtual Domains still need to be setup in DNS, maybe
> even with an MX record, correct?
Sorry - I started to laugh for a moment.
Then I realized that the 'world at large' has over or mis- used the term
'virtual' to the point of confusion.
Simply put: 'virtual means that the next word is a lie'.
By itself, that is true but not helpful.
> I mean, how is Exim in Rome going to
> receive mail from somebody@??? in Miami unless the Virtual Domain
> can be found in DNS (per MX record?) correct?
>
> Thanks,
> Robert
>
>
Exactly.
From the viewpoint of DNS entries, there is nothing 'virtual' about it.
DNS entries must exist in at least one published name server, preferably
several. They do not 'exist' if they are not *publically* resolvable, so there
is more to it than just running one of your own locally.
Otherwise, it might be more accurate to call them 'imaginary' domains.
;-)
As a minimum, at least one domain should have a 'full' set of DNS entries,
especially including a PTR record to a fixed-IP.
Only the entity controlling the router tables for the IP block can emplace a PTR
record that 'works'. (Usually your upstream bandwidth or data center provider).
This identity can be your 'mothership' - the one that you use for HELO/EHLO on
all remote-smtp outbound traffic, as at least this one needs a fixed-IP and PTR
record. Absent such, any tightly-configured correspondent MTA may reject your
submitted traffic as a probable 'zombie'.
All other hosted domains should have at least A records, and should have MX
records as well.
Not all MTA handle 'prefixes' as flexibly as Exim can do, so it is *also* a
'very good idea' to avoid use of these for differentiation unless you are going
to enter each of those into DNS records as well as the basic <domain>.<tld>.
You can manually check DNS validity very quickly with:
host <hostname>
host <IP>
dig any <hostname>
dig@<specific remote nameserver> [any | mx | ptr ] <hostname>
(this insures that a world-readable nameserver knows about your entries)
....and/or remote 'looking glass' and traceroute servers, plus several other
web-accessable DNS tools that google will find for you.
HTH,
Bill Hacker
