> On Sep 9, 2018, at 3:51 PM, Viktor Dukhovni <postfix-us...@dukhovni.org>
> wrote:
>
> In sender1's instance of the
> smtp(8) transport, the TLS policy will be mandatory for
> "example.com" recipients, while in sender2'd instance of
> the smtp(8) transport it will be opportunistic.
I should mention that this only scales when senders fall into
a *small* number of broad "classes", with each "class" having
a dedicated default transport and associated TLS policy.
sender (many) ->
sender class (a few) ->
transport + TLS policy (for many recipient domains)
What does not scale in Postfix is a large ad-hoc set of
(sender, recipient domain, TLS policy) triples.
You can class your users into three types:
* Delivery at all costs: no expectation of security
* Normal delivery: some tolerance for delays when security fails
* Secure delivery: strong preference for security, mandatory TLS
for many domains where opportunistic is observed
to generally work.
--
Viktor.
