SMTP Over TLS on Port 26 - Implicit TLS Proposal [Feedback Request]

Sat Jan 12 04:51:40 UTC 2019

Any place that has a TLS misconfig will pretty much notice it very quickly indeed

Opportunistic just means use TLS if it is advertised as available else continue encrypted.  Not sure why encountering a starttls negates it.

To the OP - what's the point of hiding the hostname in the smtp banner?  You already know from the dns. Concerned about the MTA version? You can configure postfix to claim it is exchange or avian carrier for that matter

--srs

________________________________
From: Constantine A. Murenin <mureninc at gmail.com>
Sent: Saturday, January 12, 2019 10:08 AM
To: Suresh Ramasubramanian
Cc: nanog at nanog.org
Subject: Re: SMTP Over TLS on Port 26 - Implicit TLS Proposal [Feedback Request]

On Fri, 11 Jan 2019 at 22:00, Suresh Ramasubramanian
<ops.lists at gmail.com> wrote:
> Most new MTA implementations over the past several years default to TLS with strong ciphers. So how much of a problem is low or no TLS right now?

The real problem is that opportunistic StartTLS stops being
opportunistic the minute you encounter a `STARTTLS` extension on
`EHLO`.

At that point and henceforth, TLS is pretty much 100% mandatory.

What happens if there are SSL negotiation failures? I'll tell you
what happens — the sender will receive a few bounces, X hours and Y
days after sending the mail; recipient doesn't receive anything at
all. (Unless, of course, one of the administrators would magically
decide to change the SSL options in the meantime to be compatible, or
to disable the "opportunistic" StartTLS to start with, before the
final bounce gets generated by the MTA of the sender.)

These problems are real. They're already happening today. StartTLS
being "opportunistic" is a pretty big scam.

C.
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