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I wanted to know if the format of PTR record effect the reputation of the mail server for example:-

Exmaple:-1

dig -X 162.254.148.198  (this ip belongs to mail.setopati.com)

;; ANSWER SECTION:
198.148.254.162.in-addr.arpa. 21577 IN  PTR 162-254-148-198.static.hvvc.us.

Example:-2 (this hypothetical example)

dig -X 162.254.148.198
;; ANSWER SECTION:
198.148.254.162.in-addr.arpa. 21577 IN  PTR 162-254-148-198.mail.setopati.com.

here is some of googlemail reverse record but the answer doesnt match to something like "mail.google.com" dig -x 216.58.220.37

;; ANSWER SECTION:
37.220.58.216.in-addr.arpa. 21599 IN    PTR maa03s18-in-f37.1e100.net.
37.220.58.216.in-addr.arpa. 21599 IN    PTR maa03s18-in-f37.1e100.net.
37.220.58.216.in-addr.arpa. 21599 IN    PTR maa03s18-in-f5.1e100.net.
MadHatter
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sherpaurgen
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  • I'm not sure what you mean by the *format* of the PTR record. Usually the only thing that matters is that circular resolution will complete; that is, whatever PTR record you return, it can in turn be forward-resolved to get the original address back. – MadHatter Sep 25 '15 at 06:30
  • I might have incorrect words in question, I mean the records like "maa03s18-in-f37.1e100.net." or "162-254-148-198.static.hvvc.us." .. does it matter for reputation of MailServer to have similar Rdns/ptr record.. like for domain called "linux.com" to have PTR record "mail.linux.com" in contrary to ptr record like "maa03s18-in-f37.1e100.net.", Thank you – sherpaurgen Sep 25 '15 at 06:55

3 Answers3

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I repeat my assertion above: that no-one(*) cares what the text format of a PTR record string is.

What they do often care about is that you have a PTR record associated with your server's IP address, and that whatever PTR record you return for that address, it can in turn be resolved to give an A record that points back to the original IP address.

(*) Actually, anyone may care. It's up to a mailserver admin on what factors (s)he bases the accept/reject/misfile decision taken for each incoming email, and I suppose (s)he could decide that PTR records that didn't include (say) flower names were the sign of an invalid sender. You couldn't do anything about such a choice, if it were made, but it would be an uncommon choice (to say the least) and it would find little support in the community if the server admin were called upon to justify it to the owners of the server. So, too, in my experience, would be restrictions on the text format of a PTR record.

MadHatter
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  • s/(s)he/they)/ :) – user9517 Sep 25 '15 at 07:11
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    @Iain Good Morning, you ! I personally loathe the neologistic use of the plural as a genderless singular, but I accept the need for non-gender-specific pronouns, particularly in sex-skewed professions like sysadmin. I'd really prefer the old *sie/hir* usage, but absent wide acceptance of that, what's a chap(ess) to do? – MadHatter Sep 25 '15 at 07:16
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There are say...4 factors... the only direct detriment to reputation is Dynamic PTR of IPv4 and FCrDNS for IPv6

  1. Dynamic vs Static PTR, if you have a static PTR that's better than a dynamic one, that will get you some positive points on systems like spam assassin or rbl's like rfc-ignorant.

  2. FCrDNS, beneficial for things like Opportunistic TLS, logs, netflows, etc.

    mail.example.com. IN A 162.254.148.198 198.148.254.162.in-addr.arpa. 21599 IN PTR mail.example.com.

  3. What about SPF? do you use PTR in your spf record? If you do, DON'T.

5.5. "ptr" (do not use)

This mechanism tests whether the DNS reverse-mapping for exists and correctly points to a domain name within a particular domain. This mechanism SHOULD NOT be published. See the note at the end of this section for more information. - RFC7208 Section 5.5

  1. IPv6!!!! Now nobody even touched on this for email, you must have FCrDNS for IPv6.

The sending IP must have a PTR record (i.e., a reverse DNS of the sending IP) and it should match the IP obtained via the forward DNS resolution of the hostname specified in the PTR record. Otherwise, mail will be marked as spam or possibly rejected. -Google.com

1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. 1h IN PTR mail.example.com.
mail.example.com. IN AAA 2001:db8::1
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Jacob Evans
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Mail server reputation is not a standard thing (altough there's some RFC like RFC7073 that aim at standardizing it but it doesn't event mention the PTR record)

So it is not possible to answer this question, since each spam-protection system will have it's own set of rules to evaluate the reputation of a mail system.

As said by MadHatter, the only "official" thing is that the record returned by the reverse lookup must resolve to the original IP.

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JFL
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