[67293] in North American Network Operators' Group
Re: question on ptr rr
daemon@ATHENA.MIT.EDU (Suresh Ramasubramanian)
Sat Feb 7 06:35:09 2004
Date: Sat, 07 Feb 2004 17:03:05 +0530
From: Suresh Ramasubramanian <suresh@outblaze.com>
To: garrett.allen@comcast.net
Cc: nanog@merit.edu
In-Reply-To: <020720041125.25654.2206@comcast.net>
Errors-To: owner-nanog-outgoing@merit.edu
garrett.allen@comcast.net [2/7/2004 4:55 PM] :
> this may be deemed off topic - if so apologies in advance. however i respect many of the opinions i see here so thought i would take a chance and ask.
>
> we are a stub network, injesting about 30k emails daily. about a year ago we implemented a spam filtering product. it works well. recently we turned on the knob to enable it to do reverse lookups. only the mild version, a reverse is made on the ptr rr for the ip address sending the email. if it fails the spam filter issues a 421 and closes the connection. unfortunately, we have 6 sites thus far that are legitimately trying to communicate with us but don't have ptr's associated with the ip address sending emails. since it obviously isn't a requirement to have one is it generally accepted to do so? any sense for how many end networks do and don't?
Having proper rDNS is a good thing, strongly recommended but definitely
not required for sending mail.
There are quite a few sites (including the freebsd.org mailserver, and,
on a case by case basis, even AOL) that do refuse mail from IPs without
rDNS, but turning on a "must have rDNS or you can't email us" setting
will definitely result in a non trivial amount of false positives.
--
srs (postmaster|suresh)@outblaze.com // gpg : EDEDEFB9
manager, outblaze.com security and antispam operations
