Re: Last Call: SMTP Service Extension for Secure SMTP over TLS to Proposed Standard

> I guess I'm of the opinion that such knowledge must be explicitly configured 
> if MTAs are going to fail if it is not accurate - MTAs should not be making 
> guesses.
Disallowing this sort of caching makes autodiscovery a losing strategy
in any environment which includes active attack as part of its threat
model. I suspect that we'll have to suck that up but we should do
so conscious of the tradeoff.

-Ekr