Grant Taylor via mailop <mailop@mailop.org> (Sa 25 Mär 2023 00:33:32 CET): > On 3/24/23 4:01 PM, Heiko Schlittermann via mailop wrote: > > NoListing works by causing the sending server to cascade through multiple > MXs.
> First MX either doesn't respond /or/ sends a TCP reset. Thereby causing the
> sending MTA to try the next MX.
>
> The next MX responds like normal.
Ah, ok, that's what I know as MX sandwiching.
> The cascading from one MX to the other MX achieves a very similar result as
> grey listing. But it does so in a way that is indifferent to the actual
> addresses used.
Ok, that was your point. Sure. We tried this (NoListing, MX sandwiching)
for a while and had problems when *sending* messages.
Some appliances (barracuda?) on the remote end implemented sender
verification as callback, but where stupid enough to contact the 1st MX
only (the one which did the TCP RST). As a result, they didn't accept
our mails.
> With no state to maintain it doesn't matter what the envelope from is,
> variable or static.
With our current greylisting implementation (using MAIL-FROM/RCPT-TO) as
key, we didn't have issues so far. Until mailgun started (?) using
variable senders for each delivery attempt.
Best regards from Dresden/Germany
Viele Grüße aus Dresden
Heiko Schlittermann
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