Exchange 2003 server won't auto-forward outside of the domain. Where to look?

I'm not an Exchange buff: rule-based autoforwarding works internally within our organisation but auto-forwarding to off-side addresses doesn't.

I work at a small school (400 students, 150 machines) with limited access to our network from outside. Students all have internal e-mail addresses which are often used by faculty staff. However, checking their mail from outside the school is often difficult and just adds an extra address. A number have set up auto-forwarding rules but none work. No error reports are generated either (that I can see).

Any ideas where to start looking would be appreciated.

Edit: as suggested in the title, internal auto-forwarding does work.

From serverfault Philip

• KB266166 to the rescue! :-)

  Philip : Bingo. Thanks a lot!
  From Graeme Donaldson