Abstract: The present invention is directed to an enhanced Message-ID for an email message produced by an enhanced Message-ID generator and validator of an email system. The enhanced Message-ID comprises a symbolic name used to identify the presence of an enhanced Message-ID header, a timestamp value indicating when a modification was applied to the header, an original value of the Message-ID header, and a textual representation of a one-way security hash generated from the timestamp value, the original value, and a secret phrase.

Abstract: The present invention is directed to providing mail system administrators with the ability to choose the members of a key set used for storage and retrieval of greylisting records, wherein the key set members are derived from information concerning an SMTP transaction, such as SMTP client network details and/or other SMTP command arguments in addition to those of MAIL FROM: and RCPT TO:. The invention is further directed to the specific treatment of a key set that uses a client PTR record obtained from a DNS query based on an IP address of a connected SMTP client.