Outlook 2003. Stop checking fax numbers when validating email addresses

Running Office 2003 Professional on Windows XP SP2.

Whenever I create a new email and add names to the to: or cc: fields, and then “check names” (ctrl K), Outlook will automatically fill in any entries (that are unique). The problem is, even if I use a unique name, if I have a fax number in that contact’s information, Outlook gives me the choice to email or fax the person. I never, ever use the online fax option so I want to just disable Outlook from treating fax numbers as valid addresses.

I can’t find anything in Office Help (surprise) on how I might do this. Any ideas?