Nolisting

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Nolisting is a method of defending electronic mail users against e-mail spam. The idea is that by having a non-existant primary mail server and a working secondary mail server, attempts to send an email to the primary mail server will always fail. If the mail is legitimate, the originating server will then try to send it to the secondary mail server, and should succeed. If the mail is from a spammer, it will probably not be retried. However, spammers are known to bypass the primary mail server anyway and go directly to the secondary mail server. This is because secondary mail servers often have much looser spam filters and security checks and spam that would get blocked by the primary often is accepted by the secondary.