[Exim] SMTP Authentication Woes.

I'm running FreeBSD and have installed Exim using the ports system. As I
understand it, this builds Exim with support for plaintext and cram_md5 SMTP
authentication.

I added the following to my Exim configure file and then did a HUP on the
Exim daemon:

host_accept_relay = 127.0.0.1 : <our IP range>

fixed_cram:
    driver = cram_md5
    public_name = CRAM-MD5
      server_secret = ${if eq{$1}{ph10}{secret}fail}
    server_set_id = $1

Now, in an Outlook client, I set Outlook to require authentication, then
popped in the FreeBSD credentials. I continually receive the error message:

"The message could not be sent because one of the recipients was rejected by
the server. Server Response: '550 relaying to <email address> prohibited
by administrator'."

Locally, the SMTP server works great.

What the heck is going on?

Robert Sparks
Network Administrator
M3 Design, Inc.
rsparks@???
(512) 218-8858