21 lines
1.3 KiB
Text
21 lines
1.3 KiB
Text
Spam is the black plague of the Internet world and this Sendmail milter
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attempts to address a small subset of the problem by verifying that the
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sender's email address is in good standing by performing an SMTP callback
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to the MX server responsible for the sender's domain. This milter is not
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intended to be a complete solution to spam and so it should be used in
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conjunction with other tools such as DNS blacklists and content filters.
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To be in good standing, the MX server of the sender must be reachable and
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willing to accept email for the sender from the Delivery Status
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Notification (DSN) address, which is the null address <> used for error
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reporting. This particular requirement is similar to using the
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RFC-Ignornant DSN Blacklist.
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During the callback, any failure in establishing an SMTP connection such
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as no DNS entry or the primary MX server is unreachable, or during the
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SMTP dialogue such as not accepting the DSN, user unknown, or mail box is
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full, etc. will result in the incoming mail in question being rejected.
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In the case of a temporary error during the SMTP dialogue with the
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sender's MX server, milter-sender will reject the current message with
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a temporary error code, which the sender is then free to retry again
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later. DNS lookup and connection problems are treated as temporary errors.
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