This very clearly says that SHOULD is not effectively REQUIRED at all, and is fact nothing more than RECOMMENDED. Really not sure how you misinterpreted this so badly

It's not required but they need to understand the implications. In this case the implication is that Google drops the mail. So clearly they didn't understand the implications.

Yes, but this might be googles fault for not respecting/missinterpretating the spec.

So you agree that calling it a requirement is wrong?

You should read it again.

Are you recommending they read it again or requiring it?