If your computer is set to receive faxes, but only receives the first few pages of a multiple-page fax, update to Mac OS X 10.3.9 or later.
This could happen with Mac OS X 10.3 through 10.3.8 and a Mac that has a "Jump" modem (included with Macs introduced after March 2004).
Download and install the Mac OS X 10.3.9 Update.