I have verified that this package works for ppc64.
Please add the ~ppc64 KEYWORDS to mail-client/mutt-1.5.6.
my USE Flag is "gtk2 altivec ppc64 -gnome cjk jpeg gif png tiff truetype".
Thanks, I added ~ppc64 to mutt-1.5.6-r2.ebuild. That's a slightly newer version than you mentioned. Please reopen if that's a problem.
works for me ... stable on ppc64, thanks Yuta.