purpose of PTR record ?

[Rob Mortimer]

On Mon, 01 Dec 2003 23:19:40 -0500, Andrew <andrew at arda.homeunix.net>
wrote:

>PTR records map IP addresses to names, thus doing the reverse of A records.
>
>One use of PTR records that is being used more and more nowadays is to 
>verify the identity of mail servers before mail is accepted from them. I 
>know of more than one ISP that will not accept inbound mail from any 
>host that does not have a PTR record.
>
>The degree of extra security this provides is debatable, but people are 
>doing it nonetheless.
>
>Andrew

The RFC for mail servers requires a reverse record. As the authority
for the PTR record resides with the ISP (owner of the IP address) and
not the owner of the domain name this allows those of us that run mail
servers to destinguish between a fully configured mail server and some
muppet useing an SMTP engine to by-pass his ISP's mailserver to send
SPAM from an ADSL connection in his bedroom. This assumes that the ISP
does not set reverse records for it's dynamicly allocated IP address
pool.

NB Join any campain for revese MX records NOW. Reverse MX records are
the obvious answer to SPAM as they would allow the owner of the IP
address to state exactly what domains the IP address could send mail
for, there  by closing open relays.


>
>
>mark wrote:
>
>> forward records, like name A maps to IP address w.x.y.z pretty much
>> solves the name resolution issue.
>> 
>> what is the extra or special stuff that reverse PTR records are trying
>> to achieve.
>> 
>> is this true that one of the reasons for this may be:
>> "for Chat and FTP servers it is useful to restrict access to hosts in
>> certain zones"
>> how is this restriction implemented ? (if the above is true)
>> 
>> 
>
>