Do I really need an MX record? (for e-mail to work)

sm5w2 at hotmail.com sm5w2 at hotmail.com
Thu Mar 2 04:23:38 UTC 2006


Christian Smith wrote:

> Yes, this IP address has no PTR record. mail servers which perform
> reverse DNS verification will reject mail being delivered from this IP
> address.

I am the OP for this thread.

The comment above is (in my experience) wrong.

>From 1997 until December 2005, our SMTP server was operating from a
fixed IP address (the same address actually, for that entire time).
Our domain also had an MX record.  What I didn't realize was that there
was no working rDNS for our SMTP server's IP address (it probably was
never set up).

Starting maybe some time in 2004, we began to notice that some (maybe
1/2 dozen) different recipients were rejecting our mail because of the
lack of an rDNS.  Most of these recipients were located in Europe and
far east.   Our ISP at the time was Telus, and since they basically
stopped sending us a bill for our dedicated 64-IP address block in
early 2004, I wasn't going to rock-the-boat and open a ticket for this
issue.  We used alternative means to send e-mail to the very few
affected recipients.

When we switched ISP's in Dec 2005, we went to a single static IP and
now run our network behind a nat-router/modem.  The rDNS for our IP is
some generic string that looks like it belongs to a dynamic pool - and
there's no way for us to change it.

It was only a matter of a few weeks running like that did we discover
that a moderate number of recipient SMTP servers were rejecting e-mail
being sent from our machine - because of the presence of "ppp" in the
rDNS.  We have since configured our office computers to send e-mail
through the outgoing server of our ISP.  Incoming is still handled by
our own server.

We are still running without an MX record, and the amount of spam that
we receive has dropped from 50 per day (on our old connection) to about
10 per day.  The spam we are receiving (zombie spam) is showing a
commonality in sender and/or subject, which to me indicates that the
same 1 or 2 spammers are responsible - because they are obviously
resorting to the A record, while all the other spammers are either
sending spam to our old (defunct) IP or are giving up because their
zombie or proxy trojan software is not falling back to the A record.



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