Disable authentication for submission service

[dovecot at ptld.com]

> Are you sure?  I know that postfix can use the same backend database
> for authentication as dovecot, and dovecot can be the master, but 
> dovecot
> does NOT listen on port 25 or 587 at all, those are all just used by
> Postfix.

Not true anymore. Dovecot added a submission service in a recent 
version.
Dovecot can listen on 587, take the email, and pass it on to postfix to 
then go out to the world.

https://doc.dovecot.org/admin_manual/submission_server/