Re: [Uta] SMTP Over TLS on Port 26 - Implicit TLS Proposal

[Jim Fenton <[e-mail]>]

On 1/5/19 7:05 PM, Alice Wonder wrote:
> Well since SMTP is point to point, if you depend upon encryption you
> need S/MIME or PGP and always will.

Yes, and remember that S/MIME and PGP only encrypt the message body.
There's still quite a bit of information in the message header and SMTP
transaction that aren't covered.

>
> Also I seem to recall talk of an e-mail header clients can add that
> tell a MTA not to forward it without encryption.

That's REQUIRETLS, which does this with an SMTP option rather than a
header field (there is also a header field for the opposite request, to
ignore MTA-STS and DANE).

https://datatracker.ietf.org/doc/draft-ietf-uta-smtp-require-tls/

-Jim