On Wed 09/Jan/2019 20:16:27 +0100 Ted Lemon wrote:
Port 26 requires new operational behavior, so it's not simple. It
knowing that it's available, and trying it. It requires making it
It requires deploying lots of new software.
I don't think software is a problem, because on my server (Courier-MTA) I
do it without even changing a line of code. Just duplicate 465 settings,
change port number and mandatory login. For sending, I'd need to set
routes, which is annoying; adding one line of code is handier.
And it requires allocating a reserved port, and reserved ports are
Yes. And publish an RFC.
So that's not a good reason to do it: essentially we are doing a lot of
work in order to accomplish something that we could already accomplish
existing software and doing no new work.
Wouldn't the final scenario be better?
On Wed, Jan 9, 2019 at 2:11 PM Alessandro Vesely <vesely(_at_)tana(_dot_)it
On Tue 08/Jan/2019 19:43:25 +0100 Ted Lemon wrote:
> On Jan 8, 2019, at 12:23 PM, valdis(_dot_)kletnieks(_at_)vt(_dot_)edu
>> Hint: If starttls is subject to a downgrade attack, what prevents
>> against the same pair of hosts attempting smtps instead?
> IOW, if the server is only listening on port 26, and the client is
> MITM'd, the attacker can listen on port 25 and then tunnel the
> connection to the server's port 26. Only if the client knows that
> supports TLS can you prevent a downgrade, and then STARTTLS works
> you need some secure way of signaling this, e.g. DNSSEC, and if
> then you don't need a second port allocation.
Correct. So doing port 26 wouldn't get us more security. However,
seem to get less security either. I don't see it as a useless
looks rather like a simplification to me.
Valdis' citation about 60% of SMTP servers is also correct, but
shouldn't be a problem. I'd change the line about naming to:
If a mail server support port 26 (smtps), then they MAY (was
name their MX server with "smtps-" prefix.
Prefix should never be checked automatically. Admins every now and
at MX names, and if they start to see those prefixes, they may
activate their server test-port-26 option. Gullible, eh? However,
certainly more complicated and costly. For one thing, you have to
pay an extra
mta-sts.example.com <http://mta-sts.example.com> certificate
already afforded a wildcard). For
clients it's much much more work.
*Port 26 is simple*. Straightforward for servers that already
No-brainer for clients. The only risk is connection timeout on a
non-interactive job. Does it hurt?