[exim] using port 587 for submission?

Hi,

starting with the example configuration, what do I need to do to set up
exim for relaying messages from MUAs which should be allowed to connect
from the internet and from the LAN to the mail server on the LAN?

It seems to me that the example configuration already has some things in
place for this, and that I need to somehow make it so that the MUAs can
authenticate themselves. Of course, the connections should be encrypted.

I haven't found a guide to this yet. What are best practises to do
this? A pointer to a good documentation about this, and any hints,
would be greatly appreciated.