[Exim] bsmtp delivery

I have been trying to get email deleiveredd to a school that is using
Microsoft Exchange Server from our Exim mail server.

I have tried using the BSMTP configuration in the config.sample files -
C037 - but to no avail.

In my configure file I have the following settings:

In the Main Configuration Section, I have the following settings (in
addition to the standard ones):

    smtp_etrn_hosts=bsmtp.thenet.co.nz  # the DNS record points
bsmtp.thenet.co.nz to our mail server
    smtp_etrn_command = /etc/exim/etrn_script $domain

In the Transports Configuration settings, I have the following:

    # BSMTP Transport taken from config example C037
       bsmtp_for_etrn:
      driver=appendfile
      file=/var/spool/etrn/${domain}
      user=mail
      group = mail
      bsmtp=domain
      check_string = "."
      escape_string = ".."
      prefix = ""
      suffix = ""

In the Routers Configuration I have the following:

    # BSMTP Router taken from C037
etrn_already:
 driver = domainlist
  transport = bsmtp_for_etrn
  require_files = /var/spool/etrn/${domain}
  domains = bsmtp.thenet.co.nz
  route_list = *

etrn_delay:
driver = domainlist
transport = bsmtp_for_etrn
condition = "${if >{$message_age}{1800} {yes}{no}}"
domains = bsmtp.thenet.co.nz
route_list = *

Unfortunately, while mail is delivered into the mail box
(/var/spool/etrn/bsmtp.thenet.co.nz) it is undeliverable to the school.
When The school attempts to log on, the mail is not delivered.

If I run the etrn_script from the command line, it wipes the mail box
but still doesn't deliver the mail. The next time mail is attempted to
be delivered to the mailbox, an error is returned which basically
freezes the mail because there is no file in /var/spool/etrn/ to take
the mail. I have to touch the mailbox to allow the mail to be delivered
to it again.

has anyone got any ideas. I've been battling this now for over a week.

Needless to say the school is getting pretty pissed off that they
haven't been able to get their email.

Regards
Martin