cyrus + postfix + lmtpd questions

[Diego Ventrice]

I just want to get this straight. Please, someone clarify his to me.
Consider Cyrus and Postifx runing on different servers and having to
communicate with each other through lmtp.

1)
Here´s the line we all know from cyrus.conf that is gonna bring lmtp
listening on tcp:

lmtp          cmd="/usr/local/cyrus/bin/lmtpd" listen="lmtp" prefork=1
maxchild=100

Is that enough on the cyrus side ?

2)
posfix's main.cf :

mailbox_transport = inet:[1.2.3.4]:24

3)
On some previous reply someone wrote about adding the following to
relay_domains :

example.com     lmtp:unix:public/lmtp    # for a local LMTP socket
example.com     inet:[1.2.3.4]:24        # for a remote LMTP socket

and then to extend transport_maps:

transport_maps=hash:/etc/postfix/transports,hash:/etc/postfix/relay_domains.

Cant figure out why this is necesary.

4)
And last but not least. How postfix authenticates in anyway so Cyrus ????

Thanks for all who answered and for the patience
Diego