Here is the code I used for testing. It would work for txt, pdf and docx but not tif or tiff.
C:\fax>type fax.vbs
Set FaxServer = WScript.CreateObject("FAXCOMEX.FaxServer")
FaxServer.Connect "my-fax-server"
Set FaxDoc = WScript.CreateObject("FAXCOMEX.FaxDocument")
FaxDoc.Body = "faxtest.tif"
FaxDoc.Recipients.Add ("4151234")
JobID = FaxDoc.ConnectedSubmit(FaxServer)
C:\fax>
The problem is tif file association and here is my fix.
[HKEY_CLASSES_ROOT\TIFImage.Document]
@="shimgvw.dll"
[HKEY_CLASSES_ROOT\.tif]
"Content Type"="image/tiff"
@="TIFImage.Document"
[HKEY_CLASSES_ROOT\.tiff]
"Content Type"="image/tiff"
@="TIFImage.Document"
