Dear postfix,
I don't seem to get the idea of submission, I know I must be wrong, b/c
so many articles out there preach to use a different port for
submission, but I hope to find some argument in your replies that will
make me change my mind.
If I understand correctly, submission is a means for mail server admins
to enforce some policies on port 587 w/o interfering with mail relay
which occurs on port 25. These policies are mainly :
1/ Force TLS on all incoming connexions
2/ Force users to authenticate
While 1/ can't be enforced on port 25, 2/ can be enforced for relay,
e.g. with :
smtpd_sasl_auth_enable = yes
smtpd_relay_restrictions = permit_mynetworks,
permit_sasl_authenticated, reject_unauth_destination
So the only thing that I need submission port for seems to be to force
TLS connexions, right ?
Anything else I am missing there ?
Another claim for submission is that it reduces spam, but to my
understanding that's only for *sending* spam (relaying), and that's
because the admin enforces user authentication for relay, which can
safely be done on port 25 anyways (otherwise we'd be an open relay). As
for *reciving* spam (we're the final destination), it can still be
delivered unauthed from port 25, so that won't stop *receiving* spam,
will it ?
I'm all confused.
Yassine.
