On Tue, Dec 13, 2022 at 8:45 AM Jim Fenton <[email protected]> wrote:

> This is interesting and surprised me a bit. I had expected that the
> senders of the messages being replayed were the large consumer mailbox
> providers, because it would be easy for spammers to hide in a large crowd
> and because the reputation of the large mailbox providers is (I expect)
> fairly bullet-proof just because of their size.


I can't speak to whether large consumer mailbox providers' signatures are
getting replayed, but with the scale of replay spam we're talking about -
on the order of billions per day, at its peak - that's probably enough to
make a difference in reputation for even the largest MBPs.


> Is there anything that you can say about the types of domains whose
> reputations are suffering as a result of replay attacks? Are they, for
> example, small consumer mailbox providers, email sending providers, or
> services that for some reason allow third parties to send (presumably
> transactional) email through their servers?
>

Predominantly ESPs, but really anyone with substantial sending volume and
good reputation on the d= domain. ESPs seem to be the primary target
because they tend to have the highest sending volume, so the attacker can
send more replays before reputation and deliverability degrade.
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