rDNS

Reverse DNS. The reverse DNS is a service that returns a name assigned to an IP Address.
An IP Address can be used by many domain names. The rDNS name is the true name, the rest are aliases, or "knick-names"

Apparently there is a requirement that a mail server identify itself with it's rDNS assigned name when it attempts to deliver e-mail.
The receiving mail server can verify this name against the IP Address to see if can trust the sending mail server. It is estimated by some internet posters that 80 percent of the incoming spam has bad rDNS data.

Unfortunately there are still too many real mail servers with misconfigured rDNS for many mail servers to use this easy method of sorting out spam.

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CategorySpamCopGlossaryWikiR
CategorySpamCopBlockingList

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