mail-filter/spamassassin-fuzzyocr uses giftopnm, jpegtopnm, pngtopnm, bmptopnm, and tifftopnm. media-libs/netpbm needs to be built with jpeg, png, and tiff USE flags in order for jpegtopnm, pngtopnm, and tifftopnm to be built.
Created attachment 170161 [details, diff] Possible fix
Thanks for the report! And sorry for the delay I've just added 3.6.0 in tree, with USE-dependencies fixed on netpbm