
Can we have SPF-like “CNAME invalidation records”, please? - voidz
https://noagenda.ninja/2017/03/can-we-have-spf-like-cname-invalidation-records-please/
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erkose
Why don't you try an SNI filter.

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voidz
This only mitigates http(s). Email still points to us; looking up the foreign
domain's MX records also returns the CNAME. This is particularly nasty. And,
all other services of course also end up on our server. So the problem isn't
just with http(s): it's with every service.

