Subject: Re: [Uta] SMTP Over TLS on Port 26 - Implicit TLS Proposal
From: Grant Taylor <[email-masked]>
To: [email-masked]
Date: Sat, 5 Jan 2019 22:54:34 -0700
List-Id: UTA working group mailing list <uta.ietf.org>

On 1/5/19 10:28 PM, Alice Wonder wrote:
> Requiring TLS is pointless if the MX record is not secure.

I'm inclined to disagree.  -  I see value in requiring TLS via STARTTLS 
even if the MX record wasn't secured.  -  I say inclined because I can't 
articulate the combinations of unmodified / modified MX record in 
conjunction with all the other possibilities that connections can be 
tampered with.  Be it hijacking / route poisoning / simply filtering out 
STARTTLS but not altering anything else.

> That's why MTA-STS needs the https component, to secure the MX record 
> when DNSSEC is not used to do so.
> 
> When DNSSEC is used, DANE then is better at securing the connection so 
> MTA-STS is only needed when the server and/or client do not support DANE 
> for SMTP.

I disagree.

I believe the value of MTA-STS (and HSTS) is the ability to signal that 
SMTP (HTTP) should -ONLY- be conducted over a secure connection via 
STARTTLS (TLS).  Meaning that SMTP (HTTP) should fail if there isn't a 
secure connection.

The signaling of this fact is what makes MTA-STS so valuable to me.  To 
me, the other aspects of DNSSEC / HTTPS are simply infrastructure 
necessary to enable delivery of the STS signal.

-- 
Grant. . . .
unix || die