This point where you are stuck is a mapping of an incoming email to be sent as a fax. It maps an attachment file to be sent as fax.
From the web interface go to Structure => Content Types => Add Content Type
Name = fax
Title field label = fax
Click SAVE AND ADD FIELDS. THIS WILL OPEN ANOTHER FORM.
*** Add 3 new fields as follows ***
Label = to Field = to Field Type = text
Label = from Field = from Field Type = text
Label = file Field = file Field Type = file
Go to Structure => Feeds Importer => Mailhandler nodes
In the Processor field make sure Fax Processor is selected.
Click Mapping in fax processor.
Make sure that your to, from and file fields are correctly mapped as follows:-
toaddress = to
fromaddress = from
attachments = file
IF IT IS SHOWN AS ABOVE, THEN GO TO NEXT STEP, OTHERWISE PREVIOUS STEP IS NOT CORRECT.
Go to Content => Add Content => Mailhandler Source
Enter a Title and select the Mailbox you created for your mail handler
.... so on.