[GRLUG] SMTP reverse DNS validation

[L. V. Lammert]

On Thu, 23 Apr 2015, Mark Farver wrote:

> Not sure what you are saying...did you get more than one result to a PTR
> lookup?  Can you paste dig output displaying the condition?
>
MX
crownpack.com.		2841	IN	MX	10 cpbsvf01.crownpack.com.

;; ADDITIONAL SECTION:
cpbsvf01.crownpack.com.	2841	IN	A	67.221.227.25

;; ANSWER SECTION:
25.227.221.67.in-addr.arpa. 3600 IN	PTR	cpbsvf01.crownpack.
25.227.221.67.in-addr.arpa. 3600 IN	PTR	67-221-227-25.xiolink.com.

> Requiring anything beyond the existence of a PTR record on an incoming
> message is problematic.  You can certainly give positive score to a machine
> with valid and identical forward and reverse records but many legitimate
> senders will not have that.
>
They may be a legitimate sender, .. but an invalid reverse DNS PTR does
indicate they may *not* be legitimate and our email servers are configured
to reject.

The problem is that MXToobox only checks for the existance of a PTR record
and does not match the hostname. I have since found a way to accurately
show the discrepancy: http://www.debouncer.com/reverse-dns-check

	TFTR!

	Lee
-------------- next part --------------
_______________________________________________
grlug mailing list
grlug at grlug.org
http://shinobu.grlug.org/cgi-bin/mailman/listinfo/grlug