Graylisting

Graylisting is a way to automatically block spam. It is based on the fact that the behavior of spam software is often different from that of ordinary e-mail servers. If the recipient’s e-mail server refuses to accept the e-mail and signals a temporary error, the sending server must wait and try again later. Spamming applications, however, are usually unwilling to do so.

How can I avoid being graylisted?

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