Canon IRC 2880/3380 Scan to Email client

We have three Canon IRC Printer Scanners that will quite happily scan to pdf and transmit the document via exchange to both internal and external recipients - problem:- the internal recipients can read the "attached image" but all external recipient get a smaller pdf file of the same name that it totally blank when opened.
If the internal recipient forwards the mail to the external recipient then the pdf is received at full size and can be read OK.
This problem arose after the SBS 2003 SP2 (with Exchange SP2) crashed and was fully reistalled with all users etc. However as we are going to transition shortly I have left the new install at SBS 2003 SP1 with exchange at SP0.
Any Ideas?
Canon is baffled as are their local reps.

John Gardner