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Re: [ietf-smtp] SMTP Greylisting Retry Hints + PRDR

2019-02-08 02:43:53
On 2019-02-07 23:20:24 +0100, Dilyan Palauzov wrote:
the problem with bounces is, that they can lead to blacklisting the
server, that generated them.

Right. Bouncing spam is never a good idea, IMHO.

What I drafted, which has nothing to do with grey listing, is not
necessary non-standard and avoids the problem with backscatters.  The
“retry=” hint mitigates the side effect of delayed arrival.

Yes, the retry hint can mitigate this. I've implemented a similar scheme
in 2005. I thought about delaying all recipients except the first but it
was impractical. The RFC allows up to 100 recipients and at the time
this was actually quite common. With typical retry times between 15
minutes and 2 hours, the last recipient would have gotten the mail
between 25 and 200 hours later (and probably not at all in the latter
case since 200 hours is longer than the typical queue timeout). A retry
hint "try again in 2 seconds" would have made this practical *if* it had
existed *and* been widely implemented. 

What I ended up doing was implementing a heuristic to guess which
recipients would produce the same result and delaying only those which I
expected to differ from the first one. Ugly, but worked actually quite


   _  | Peter J. Holzer    | we build much bigger, better disasters now
|_|_) |                    | because we have much more sophisticated
| |   | hjp(_at_)hjp(_dot_)at         | management tools.
__/   | | -- Ross Anderson <>

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