[Exim] does a smarthost need a password?

I have looked for the following problem on the FAQs, but have found
nothing. If the question is completely wrong, please direct me
to some documentation as easy as possible.

PROBLEM:

I am using exim on a machine connected to an ISP via ppp.
I have an account on another machine, and I want this machine to work as a
smarthost, for all non-local messages. I set up this via eximconfig, but
it does not work (the mailservers denies to relay, error 550). I guess one
has to specify his account username and password on the smarthost. If this
is true how can I specify this data?


Thank you
Alessandro