Doc pointer request

[David Favor]

At one point seems like I found a write up in
the Dovecot docs about having Dovecot directly
listen on port 25 using Opportunistic TLS along
with port 587 authentication, so only Dovecot was
required to handle incoming email.

Said another way, no requirement for Sendmail,
or Postfix or EXIM.

Just straight up Dovecot.

If I'm remembering correctly, someone point me
to the correct docs for this setup.

Thanks!