> On Apr 3, 2017, at 5:23 AM, <[email protected]> 
> <[email protected]> wrote:
> 
> Regarding the policy validation, would't the use of DNSSEC fix both the
> validation and update on demand problem?

Quite so, but with DNSSEC you don't need STS, just use DANE.

> In the SAN vs MX discussion, if I'm not wrong, the discussion is
> either to use the mx parameter from the policy to filter MX
> hostnames, or to use it to filter against the SAN within the
> certificate received.

Yes, possibly renamed if ceases to be an MX hostname filter.

> Since the section 4.2 
> (https://tools.ietf.org/html/draft-ietf-uta-mta-sts-03#section-4.2) defines 
> that "... presented by the receiving MX MUST be valid for the MX hostname and 
> chain to a root CA that is trusted by the sending MTA ...", the result of any 
> of the two options would be the same (we assume that an attacker cannot forge 
> a certificate that would pass certificate validation).

That text would also change if the policy admits other matching names.

> But, using the mx parameter to filter the MX records, would create
> somehow an alternative way of discovering the list of MX for a domain,

No, it is an authenticated cached *filter* on the data obtained from
DNS, and supports wildcards, which means that you don't actually get
the MX hostnames from the policy.

-- 
        Viktor.

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