Actually, they wouldn't really know unless this domain is used. I guess they check the `Host` header to get the domain that targeted this IP and then check where the MX are hosted.

Or they just dont want to be put in the position of having to give out keys.

I think the real paranoid people use cloudHSM.

Both KMS and CloudHSM are FIPS 140-2 Level 3 and AWS claims they cannot read private keys from KMS. The main difference is KMS uses IAM and the AWS REST API while CloudHMS uses PKCS #11/JCE and a separate permissions system.

The docs say both use HSM. Under "Secure" in the accordion menu https://aws.amazon.com/kms/features/#topic-0

My understanding is that AWS KMS uses AWS designed HSMs and are tightly integrated with all AWS services while while CloudHSM uses LiquidSecurity 2 Cloud HSM adapters and use more conventional APIs

https://www.marvell.com/products/security-solutions/liquidse...

>My understanding is that AWS KMS uses AWS designed HSMs

That's my take as well reading about how they handle firmware (sounds like they're using their own chips, presumably similar to how they use other hardware acceleration and offload)