> On Feb 17, 2017, at 5:33 PM, Chris Green <c...@isbd.net> wrote:
>
> OK, so the older version is using SMTP STARTTLS which runs on port 587
This is how TLS has worked in MTA-to-MTA SMTP for the last > 15 years.
https://tools.ietf.org/html/rfc3207
> and the newer (>=3) version is using TLS directly on port 465.
No, Postfix 3.0 and later *also* support SMTP over TLS as used
by some systems on port 465. The submission service on 587 and
the relay service on port 25 continue to support STARTTLS.
To use submission on port 587 the server needs to provide that
service. If a server only supports "smtps" on 465, then that's
what you need to use.
--
Viktor.
