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Názor k článku DomainKeys - nová antispamová technologie od Petr Souček - RFC2821 6.1: If there is a delivery failure after...

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  • 31. 10. 2004 22:52

    Petr Souček (neregistrovaný)
    RFC2821 6.1:

    If there is a delivery failure after acceptance of a message, the receiver-SMTP MUST formulate and mail a notification message. This notification MUST be sent using a null ("<>") reverse path in the envelope. The recipient of this notification MUST be the address from the envelope return path (or the Return-Path: line). However, if this address is null ("<>"), the receiver-SMTP MUST NOT send a notification.

    RFC2505:

    2.6.1. "MAIL From: <>"

    The MTA MUST NOT refuse to receive "MAIL From: <>".

    The "MAIL From: <>" address is used in error messages from the mail system itself, e.g. when a legitimate mail relay is used and forwards an error message back to the user. Refusing to receive such mail means that users may not be notified of errors in their outgong mail, e.g. "User unknown", which will no doubt wreak more havoc to the mail community than spam does.

    The most common case of such legitimate "MAIL From: <>" is to one recipient, i.e. an error message returned to one single individual. Since spammers have used "MAIL From: <>" to send to many recipients, it is tempting to either reject such mail completely or to reject all but the first recipient. However, there are legitimate causes for an error mail to go to multiple recipients, e.g. a list with several list owners, all located at the same remote site, and thus the MTA MUST NOT refuse "MAIL From: <>" even in this case.

    However, the MTA MAY throttle down the TCP connection ("read()" frequency) if there are more than one "RCPT To:" and that way slow down spammers using "MAIL From: <>".

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