Re: IETF mail server and SSLv3

[[e-mail]]

> On Fri, Feb 05, 2016 at 06:42:34AM -0800, Ned Freed wrote:

> > > The implementation and documentation of this was joint work with
> > > Wietse back in early 2006.  These days, when STARTTLS fails, Postfix
> > > tries other MX hosts first and if they all fail, defers the mail
> > > initially. Cleartext fallback kicks in on the second delivery
> > > attempt if STARTTLS fails again.
> >
> > Actually, I consider this approach as unacceptable unless the second delivery
> > attempt occurs within a minute or two. (Which, incidentally, is a much shorter
> > retry period after deferral than the standards recommend.)

> The default is 5 minutes, with doubling exponential backoff up to
> a cutoff of somewhat over an hour:

That's borderline IMO.

> ...

> As for "unacceptable", you might find the below fall into that
> category:

>   * IIRC Sendmail never falls back to cleartext if STARTTLS is
>     advertised.

A fix has been available for a while; the apparent plan is to integrate 
it into sendmail 8.16. See:

http://www.sendmail.org/%7Eca/email/patches/tls_failures.p1#sthash.iwHHaXb0.dpuf

for details. However, since the fix doesn't allow for immediate fallback, it
leaves a lot to be desired.

> ...

> As for a delay of < 5 minutes delivering email to such broken sites
> it is, for most users, a reasonable trade-off to reduce needless
> TLS fallback in the face of routine transmission glitches.

That's a consequence of piggybacking cleartext fallback on the deferral
mechanism you use for transmission failures. It doesn't have to  be done this
way.

				Ned