Re: PTR? what the heck is it?

From: John Joot (johnjoot_at_hotmail.com)
Date: 06/09/03 

Date: Mon, 09 Jun 2003 16:20:34 GMT

thnks for the info barry...the reason why i'm asking is this... in my mail
server program, among the options, for security purposes, i am given the
following to check-mark:

1) perform PTR record lookup on inbound SMTP
    a) send 501 and shutdown connection if no PTR match

2) perform reverse lookup on HELO/EHLO commands

3) perform reverse lookup on value pased in mail command

4) refuse to accept mail if reverse lookup returns "mail not found"
    a) send 501 error code (instead of normal 451)
    b) and then shutdown connection...

what i don't understand is if there is already a reverse lookup on PTR and
shutting down option checked, why would i need to check-mark (2) (3) (4)
a&b?

i've noticed that if i check-mark all (including 4 a & b), my mail server
will reject valid emails frm my friends' work place.. ie. it would reject
the subdomains of xxx.workdomain.com since it is probably an internal domain
or just the naming scheme of a particular computer desktop in the office.

jj

"Barry Margolin" <barry.margolin@level3.com> wrote in message
news:BL1Fa.8$h8.168@paloalto-snr1.gtei.net...
> In article <Ok1Fa.26921$6f3.4826739@news1.telusplanet.net>,
>
> PTR records are the DNS entries that map addresses back to hostnames.
>
> The reason that mailers often check this is that properly-run mail systems
> will practically always have valid DNS entries. Spammers, on the other
> hand, often come from dynamically-assigned addresses that don't have DNS
> entries. So this is a crude way of distinguishing "real" mail servers
from
> home machines.
>
> --
> Barry Margolin, barry.margolin@level3.com
> Level(3), Woburn, MA
> *** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to
newsgroups.
> Please DON'T copy followups to me -- I'll assume it wasn't posted to the
group.

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