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Thursday, November 22, 2012, 14:16

Reverse DNS / PTR Records

Category: General

Solution ID: 00000172


What are PTR records/Reverse DNS records and why do I need them?


DNS (Domain Name Services) is a system that resolves Internet host and domain names into their corresponding IP addresses. The basic DNS mechanism for this resolution is the A record. For example, "" is really the IP address (as recorded in its A record).

Reverse DNS is a mechanism using a PTR record to recording the reverse mapping, i.e. mapping an IP address to an Internet domain or host name.

Many mail servers perform reverse DNS lookups in an attempt to validate a mail server and verifying the legitimacy of the sender. There are identifying elements of a mail server that are commonly queried and compared: the DNS A record, the DNS PTR record and the hostname reported by the mail server.

Different mail servers will apply different degrees of strictness with respect to these values. Often mail server connections will be refused if a PTR record does not exist for a mail server. Other servers will compare the values associated with A records, PTR records and the reported hostname of a mail server and apply spam scores based on the discrepencies between these values.

The best practice is to have the A record, PTR record and hostname of your mail server or PerfectMail anti-spam server all use the same name to ensure there are not validation issues.

Tags: reverse, dns, ptr, record, domain, name, resolution, mail, server, configuration

See Also:

Link to this article: kb/reverse_dns_ptr_records

Updated: Thursday, November 22, 2012, 14:16

-- David Rutherford


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Last modified: 2014-02-28, 14:00

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