ietf-smtp
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Re: 2821bis/ter and procedures

2008-08-08 15:42:41

Tony Finch wrote:
On Fri, 8 Aug 2008, Frank Ellermann wrote:
Also different from what I had in mind.   IOW it really deserves
a clarification.  I wonder if this could be coupled with the
"selective reject" ideas (draft-hall) posted here a year ago.

No, it's hard enough to clarify retries without introducing new
complexity.

Tony.

I'm having a hard time why the solid SMTP state machine driven by 4yz, 5yz reply codes is being question now.

For me, there are only a few technical goals for all retry strategies:

  - Understand when delivery (or bounce) is required - not an option,
    in fact, understand there might be legal requirements and there
    is a risk to behave with negligence and malpractice.

    Depending on the type of message, including who owns it,  only
    the client can decide how important is satisfying delivery
    expectations.

  - Don't send duplicates, and

  - Don't bother trying forever when you continue to get the
    same results over an extended reasonable time.

From this, IMV, all retry strategies can be modeled per site, per implementation, per software. Its a common goal we all share and its really mail network independent.

Off hand, the only pressure we got to alter our current retry strategy was to satisfy the growth of greylist systems.

Here, a new design factor was introduced to help guide a faster 2nd retry to help minimize delayed delivery due to 1st time greylisted rejected. The GreyList document recommends a 451.

However, as it was found, not all support this and common sense tells you it should not matter - a 45x means a retry is possible. So doing a generic faster 2nd retry for 45x responses proved to work better in all cases.

--
Sincerely

Hector Santos, CTO
http://www.santronics.com
http://santronics.blogspot.com

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