[OT] does deliveragent must have a PTR RR

Lyle Giese lyle at lcrcomputer.net
Tue Feb 1 03:57:56 UTC 2011

pyh at mail.nsbeta.info wrote:
> Hi list,
> I can't setup a ptr RR for my mailserver's IP.
> Here the main ISPs who are owned by this garbage state take expensive
> price for setup a reverse record for a public IP. It's about 30 USD
> each month for each IP.
> But some MTAs does require the peer deliveragent has a PTR RR,like
> AOL's email systems.
> Is there a special RFC for this requirement?
> Regards.
> Mail Delivery System writes:
>> This is the mail system at host mail.nsbeta.info.
>> I'm sorry to have to inform you that your message could not
>> be delivered to one or more recipients. It's attached below.
>> For further assistance, please send mail to postmaster.
>> If you do so, please include this problem report. You can
>> delete your own text from the attached returned message.
>> The mail system
>> <donovan at beth.k12.pa.us>: host mx1.beth.k12.pa.us[] said:
>> 450 4.7.1
>> Client host rejected: cannot find your reverse hostname, []
>> (in reply to RCPT TO command)
I do not believe this to be fully covered in an RFC, but came about as
Best Practices as we fight SPAM. The best source for the Best Practices
for this is at http://postmaster.aol.com

Wonder through ALL of the pages that this area at AOL has to offer or
you will miss some important points, like that 12 hrs is considered the
min TTL for A and PTR records for mail servers. Less than 12 hrs TTL on
these records are considered by default indicators of dynamic IP addresses.

Lyle Giese
LCR Computer Services, Inc.

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