[Exim] SMTP no accepting connetion via internet with client.

Please could someone advise me on how I can connect to my server via the
internet to send mail. It work perfectly via the local/trusted network,
but
not via the internet .
this is the error message from outlook express.
"
The message could not be sent because one of the recipients was rejected
by the server. The rejected e-mail address was
'gregory_machin@???'. Subject 'text', Account: 'greg', Server:
'mail.linuxpro.co.za', Protocol: SMTP, Server Response: '550 relay not
permitted', Port: 25, Secure(SSL): No, Server Error: 550, Error Number:
0x800CCC79
"
this is a copy of my acl what have i done wrong ?
"
begin acl

# This access control list is used for every RCPT command in an incoming
# SMTP message. The tests are run in order until the address is either
# accepted or denied.

acl_check_rcpt:

# Accept if the source is local SMTP (i.e. not over TCP/IP). We do this by
# testing for an empty sending host field.

#accept hosts = :

# Deny if the local part contains @ or % or / or | or !. These are rarely
# found in genuine local parts, but are often tried by people looking to
# circumvent relaying restrictions.

  deny    local_parts   = ^.*[@%!/|]

# Accept mail to postmaster in any local domain, regardless of the source,
# and without verifying the sender.

  accept  local_parts   = postmaster
          domains       = +local_domains
  require verify        = sender

  accept  domains       = +local_domains
          endpass
          message       = unknown user
          verify        = recipient

  accept  domains       = +relay_to_domains
          endpass
          message       = unrouteable address
          verify        = recipient

  accept  hosts         = +relay_from_hosts
  accept  authenticated = *

  deny    message       = relay not permitted
"

Many Thanks
Gregory Machin