See Faxing Formatted Files for information on converting these files into the proper format. In addition, you can fax ASCII (including Japanese EUC files if your system is so configured), PCL, PostScript, TIFF, and many other image file formats. See Supported File Types for the complete list of supported file types.
When Faximum actually sends or displays the fax it converts all files to Class F compressed TIFF files. These are bitonal (black and white, single plane) files. Color and grey scale images are dithered to achieve a grey scale effect.