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I've got some problem with ptr and domains. Here is situation:

  • external ip: 123.123.123.132
  • domain1: example.com
  • domain2: elpmaxe.net
  • mailserver is on exim4.
  • PTR 123.123.123.123 matches example.com

How should I set the PTR for the second domain? How this is solved in web-hosters/vps/? Should I have another external IP for that?

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up vote 2 down vote accepted

PTR records are mostly used for mail purposes, in order to establish some level of credibility when mail is received from another server. Therefore, for a server that hosts a mail service, they should resolve to the IP address of the MX record for that server. They are not needed for websites. All modern web servers can handle name based virtual hosts, where any number of websites can share a single IP address (on HTTP).

The picture changes when you start to use HTTPS. One limitation of that protocol is that you need to have a separate IP address for each HTTPS website.

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The answer from wolfgangsz says: "Therefore, for a server that hosts a mail service, they should resolve to the IP address of the MX record for that server" To what, or whom is the word "they" in that sentence referring? According to the rules for relating pronouns, each pronoun refers to the most recent subject, or noun preceeding the pronoun? so "they" means "a mail service" should resolve to a the IP for the server? –  user117830 Apr 17 '12 at 15:46
    
It's referring to PTR Records. –  Iain Apr 17 '12 at 21:50
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