More on PTR Records

Quite some time ago I wrote up Basic DNS: PTR records and why you care. I realized today that it is far too geeky: I sent someone experiencing a PTR issue to read that and he came back still thinking that either his Mac or Verizon were to blame.

Why does he think that? Well, I suspect mostly because he got bad support from Verizon AND Apple. His problem was that email he sent to someone with a Comcast address got bounced back with a message like this:

Comcast requires that all mail servers must have a PTR record with a valid Reverse DNS entry. Currently your mail server does not fill that requirement.

Whose mail server does not fill that requirement? His Mac Mail.app is set to use "outgoing.verizon.net" as its outgoing server. His machine NEVER TALKED TO COMCAST. It's not supposed to: it's supposed to talk to "outgoing.verizon.net". It's THAT machine or some other machine of Verizon's that will talk to Comcast. So if Comcast is complaining, it's something at Verizon they are complaining about, and nothing to do with whether or not he's using a Mac or a PC!

It's beyond amazing that no one at Apple or Verizon was able to help him with this and that they each kept bouncing him back to the other.

Specifically, Comcast rejected "206.46.173.5". I just checked and that's NOT "outgoing.verizon.net" but it is in Verizon's block, and it doesn't have a PTR record so Comcast is right to complain. Verizon needs to assign a PTR to that address and that wll be the end of his problem.

Nothing to do with OS X or anything else. Just Verizon itself.

Comments /Unixart/more-ptr.html


Thu Apr 24 17:11:13 2008: Subject: PTR records   JonR


Thanks for this, Tony. I'd never even heard of PTR records before (your original post was before I subscribed to your blog, I think). This may, unfortunately, come in handy, for my ISP is ATT/Yahoo! and they, er, make their share of mistakes. (Couldn't find the "understatement" HTML tags to use there.)

Could you state, or restate, the best way to get a situation like this corrected when it occurs?



Thu Apr 24 17:28:53 2008: Subject:   TonyLawrence


There are two ways to solve it: have your ISP make a PTR record for your mailserver, or have your mailserver relay through something that does have a PTR record.

In this case, this guy was doing the latter, but Verizon screwed up their own DNS and didn't have the PTR.


Fri Apr 25 11:30:53 2008: Subject: Mail Servers   badanov
http://www.freefirezone.org

A lot of ISPs mail admins look for mail coming from servers which have no reverse DNS entry or PTR as part of their anti spam operation, and I am always getting them to drop that requirement for my server since I don't have a full DNS setup.

Fri Apr 25 14:09:45 2008: Subject:   BigDumbDinosaur
http://bcstechnology.net

Lack of a valid PTR record is almost always a sign of a spam source. My mail server will block any foreign system that doesn't have a PTR record. If the server admin can't be bothered to handle the DNS details he/she probably isn't sufficiently motivated to police the system's usage and try to keep out the spammers. Either that, or the server has been intentionally set up to be an open relay.

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