IP4R

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E-mail

A DNS lookup that attempts to determine if a mail server is likely to be sending spam. You take the IP address of the mail server, turn it around, and query a "DNS zone", to come up with something like "2.0.0.127.relays.example.com". If the mail server is listed in the spam database you queried, it will return an answer indicating that the mail server is listed.

SmarterMail — SmarterMail Glossary