Reverse DNS and mail

[User, Public]

Hi Mike,
When a mail is sent, the sending server looks for an MX record for the
destination domain in DNS, and will open a connection to that IP address
to send the mail.  It is up to the receiving server to allow reception
of that mail depending if it is configured to receive mail for that
domain.  You can have hundreds, or even thousands, of domains configured
to be received on one mail server, with one IP address.  Each domain has
an MX record pointing to the same single address. =20

I think you are getting confused between mail clients/servers, and
forward/reverse DNS. =20

C



Christopher P. Jenkins, Senior Consultant

Concordant, Inc.

P:  508-820-3080

F:  508-820-4367

C:  508-241-7415

E:  chris.jenkins at concordantinc.com


-----Original Message-----
From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org] On
Behalf Of Mike DiChiappari
Sent: Wednesday, January 07, 2004 11:09 PM
To: comp-protocols-dns-bind at isc.org
Subject: Re: Reverse DNS and mail

> There is no requirements that the mailserver has several FQDN, it's
> better to have each domain have an MX record to
> the "one-and-only" real mailserver

Yes, but our mail server could appear as foo.com or bar.com, depending
on
who is sending email (we host both foo.com and bar.com).  So wouldn't a
recipient mail client want foo.com's IP address to resolve to foo.com
and
bar.com's IP address to resolve to bar.com?  Conversely, wouldn't an
email
client that does reverse DNS reject email where foo.com's IP address
resolves as bar.com.

Another way to ask this is that if foo.com and bar.com have the same IP,
how
does one guarantee that upon reverse DNS lookup that joe at foo.com's IP
address resolve to foo.com.  Maybe DNS will return bar.com?

> Same goes with the nameservers for the zones, there is no
> point in faking separate names of the nameservers just to
> have them coincidence with the domain itself. In fact it's
> far less work to have fewer glue-records to keep up to date.
>

Won't email appear to come from the same domain then?

Mike