GraphicsMagick is a replacement for ImageMagick. Now net-mail/libpst depends only on media-gfx/imagemagick.
Sorry about the mass reassignment, but this undertaking really shouldn't burden bug-wranglers further.
Closing this as invalid since libpst specifically checks for imagemagick.
Feel free to to reopen if you produce a patch for configure script and test to make sure graphicsmagick works as expected.