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Re: Fixing graylisting [was TBR]

2007-11-15 02:22:17

Dave Crocker wrote:


Although only a near-term, tactical benefit, greylisting directly impacts mail from bad actors. It's serious downside is that it also impacts first-time mail from good actors.

Which can be minimized, to a near "unfelt" impact by simple fine tunning of SMTP router/sender frequency tables, in particular the 2nd attempt.

RFC-2821 currently recommends/states: 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

The insights were laid out for variable (time/retry) strategies, making it possible for Greylisting to work with minimal to no significant impact.

It is when you (speaking in general) are setting there waiting or expecting a message, and it doesn't arrive is what raises the hair of people. But most people just press the "send" button and while they might expect "instant" send off because they know how their own mail system works, they won't be surprise if there isn't instant reception because they can't presume to know how the remote end works. The same concept applies in telecommunications flow controls designs.

I was really skeptical of GL, but when it was implemented right with proper fine tuning of SMTP to minimize impact, it is really one of those Ronco's "Set it and Forget it" ideas. :-)

My recommendation for 2821bis is to include some insights about or how "variable strategies" plays a bigger roles these days and in fact, might be almost an "necessity" for improved modern operations these days - thats dealing with the realities we have out there. Even if I didn't want to incorporate GL into our own system, the sending retry strategies had to be reconsidered due to increased remote GL systems.

My 2 pennies.

Hector Santos, CTO