This link has been bookmarked by 17 people . It was first bookmarked on 12 May 2007, by Joel Liu.
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18 Mar 15
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07 Jan 11
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Not every IP address has a corresponding PTR record. In fact, if you took a random sampling of addresses your firewall blocked because they were up to no good, you'd probably find most have no PTR record - a dig -x gets you no information. That's also apt to be true for mail spammers, or their PTR doesn't match up: if you do a dig -x on their IP you get a result, but if you look up that result you might not get the same IP you started with.
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21 Apr 10
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30 Jun 09
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29 Jul 08
Wesley FryerGood discussion (tho unfortunately there is a ton of ads) about PTR records, email spam, mailserver blacklisting, etc.
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07 Jul 08
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03 Feb 08
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16 Oct 07
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12 May 07
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That's why PTR records have become important. Originally, PTR records were just intended as a convenience, and perhaps as a way to be neat and complete. There still are no requirements that you have a PTR record or that it be accurate, but because of the abuse of the internet by spammers, certain conventions have grown up. For example, you may not be able to send email to some sites if you don't have a valid PTR record, or if your pointer is "generic":
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