[OT] does deliveragent must have a PTR RR

Mark Andrews marka at isc.org
Tue Feb 1 05:40:11 UTC 2011

In message <4D4784C4.2020502 at lcrcomputer.net>, Lyle Giese writes:
> 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

And is also against RFC requirements.

> 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.

You can't infer diddly squat from a TTL.  There are plenty of reasons
to want a low ttl other than it was assigned dynamically.

* I'm going to renumber my whole network because I'm switchinhg
ISP's so I've reduced my TTL's to 5 minutes to reduce the impact
of the renumbering.

* I have a warm spare in a different data center and as most client
behave badly when one of the addresses is unreachable I only advertise
one address.

More stupid unrealistic hoops to jump through.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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