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Re: 2821bis consideration - New 2nd attempt Retry Strategy recommendation

2007-11-16 00:47:45

Hi Hector,
At 15:59 15-11-2007, Hector Santos wrote:
But I want to make sure I wasn't mis-read. To be clear, the suggestion really has nothing to do with anti-spam or even mentioning it. We already have it saving: Sending Strategy


   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

This was excellent insight done at the time. Maybe that is enough, but I do believe a word smith can finesse a new clause or sentence indicating why a short 2nd attempt may be applicable and highly desirable for improved outbound mail operations. Maybe something like:

   Due to the increase of new SMTP challenge/response receiver
   systems, if the SMTP client sees 451 temporary response code
   for the RCPT or DATA state, it MAY consider using a shorter
   2nd attempt interval, recommended 5-10 minutes.  This SHOULD
   be for the 2nd attempt only.

The "451" reply code means error in processing. As it's a policy decision, a "450" reply code is more appropriate.

With the advent of greylisting, a shorter second attempt may seem desirable to ensure timely delivery of message. However, we should take into account the impact it will have on the receiver. Such a short interval conflates the problem for the receiving system if it's under heavy load. We are also assuming that the greylisting period will be under five or ten minutes. That may not be the case. For the proposed strategy to be effective, the sender would have to determine whether the temporary error was due to greylisting (status code instead of reply code) and the greylisting delay.