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

2007-11-16 08:22:11

Hi SM,

Isn't the z digit in x5z is undefined? The 1st paragraph, last sentence in 4.2.1, says:

   "The third digit and any supplemental information that may be
   present is reserved for the finest gradation of information."

I see the example literal text for 451 says "processing error", but the literals are meaningless to SMTP. Offer no flow control logic. Right?

Yes, I agree, it would ideal if a special code can be detected.  Hmmm,
the Greylist specs shows  a 4.7.1 extended code:

      451 4.7.1 Please try again later

We use the 5 minute 2nd retry interval because anything else is deemed too long for these deliberate 1st time only rejects - an action that should not occur under normal circumstances. I have not seen or heard of any negative impact due to a shorter 2nd retry interval. But there were an awful amount of reports from confused operators before we added the variable frequency table to address the increasing hits on remote GL systems.


Hector Santos, CTO

SM wrote:
> 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
>>    non-delivery.
>> 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.
> Regards,
> -sm