Re: ****Re: [OT] HELP!!! mail attack

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On Fri, 2008-03-28 at 11:15 +0900, John Summerfield wrote:
> Craig White wrote:
> 
> > You're 'not sure that a server really *has* to resend' ?
> 
> You are implying it must. What text of rfc 2821 does it violate ifit 
> doesn't?
----
A temporary fail code of 450 occurs at the RCPT stage as you know and
there is no way that the sending server can mistake this to be a
successful delivery.

A permanent fail code like 55X renders redelivery pointless and the
original sender should be notified.

As for handling re-delivery, this section covers it...

4.5.4.1 Sending Strategy

   The general model for an SMTP client is one or more processes that
   periodically attempt to transmit outgoing mail.  In a typical system,
   the program that composes a message has some method for requesting
   immediate attention for a new piece of outgoing mail, while mail that
   cannot be transmitted immediately MUST be queued and periodically
   retried by the sender.  A mail queue entry will include not only the
   message itself but also the envelope information.

   The sender MUST delay retrying a particular destination after one
   attempt has failed.  In general, the retry interval SHOULD be at
   least 30 minutes; however, more sophisticated and variable strategies
   will be beneficial when the SMTP client can determine the reason for
   non-delivery.

   Retries continue until the message is transmitted or the sender gives
   up; the give-up time generally needs to be at least 4-5 days.  The
   parameters to the retry algorithm MUST be configurable.

As to the notions of 'has to' or 'violated' sections...there is only that which is reasonable and prudent and by all custom (and the language above), it's obvious that re-delivery is expected, customary, and standard practice for all SMTP servers I have dealt with.

You are correct of course, that nowhere does it state that sender MUST attempt to re-deliver. I do wonder if you would find an SMTP server that by default didn't attempt re-delivery on temporary failures to be acceptable. It MUST be configurable - that's it. 

Craig


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