sorry I don't have the personal email of
Steve Underwood (I saw a thread of him related of this subject), it's about a problem
of spandsp txfax and jpeg files.
I didn't succeed to find the right conversion to make the far end accept the fax.
I get always "far end cannot receive at the size of the image".
this problems occurs only from jpeg to tiff conversion.
I use imagemagick for that :
 
sudo /usr/bin/convert -page Letter -density 204x196 -resize 1728x1184 -units pixelsperinch -monochrome -compress Fax <fileToConvert>  <fileToSave>
 
I tried numrous options but no luck.
 
Thanks