Check the phone number it was sent from. Most faxes have the number at the top of the page. If not look in your fax machines 'received log'. Once you locate the number try doing a 'reverse phone' look up online. You can find more information here: www.411.com
A Fax is a document that is transmitted electronically over a telephone line. Faxes can be sent from and to any telephone number. They do not require a special line. The origin of any fax can be traced simply by tracing the phone number from which it was...
Tracing a fax number isn't difficult unless the number is unlisted or if the number appears to have no owner. Look for the number on your fax that you're wanting to trace. Then go to a website such as 411.com to trace the number.