[Emailcore] Re: [Last-Call] Re: Re: Re: Re: Re: draft-ietf-emailcore-as-28 ietf last call Secdir review

[Nico Williams <[e-mail]>]

On Fri, May 01, 2026 at 05:43:52AM +1000, Viktor Dukhovni wrote:
> On Thu, Apr 30, 2026 at 10:52:30AM -0700, Christian Huitema wrote:
> > This is often implemented with compile options, such as "#ifdef
> > SUPPORT_CLEARTEXT".
> 
> Not possible with SMTP.  In a STARTTLS protocol cleartext is simply not
> optional, all that's optional is whether to allow mail transactions to
> take place while in cleartext mode or not (the latter requires
> additional code to check and refuse, while still in cleartext).
> 
> The only way to reduce the MTA's attack surface that is relevant to this
> discussion is to not implement TLS, then attacks on the code that
> provides TLS support are no longer possible.  I am not hearing voices
> in support of that.

The retort is going to be to not allow RCPT and such outside STARTTLS,
but we know we need to allow at least email so well-known mailboxes like
postmaster, and possibly that should be extensible, so basically it's
not possible to not allow cleartext email exchanges.

Also, even if STARTTLS, or a new SMTPS that uses TLS first, were
required, encryption is not enough -- we also need authentication, and
all too often today SMPT ends up using unauthenticated servers, right?

Nico
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