According to the xbiff man page, xbiff has but one bug: "The mailbox
bitmaps are ugly."  The bitmaps contained herein attempt a fix.  The
motif is that of an envelope which sprouts contents sticking out when
mail has arrived.  Looks swell in AfterStep.

Add the following to your .Xdefaults:

    XBiff*emptyPixmap:      /usr/local/include/X11/bitmaps/mail-empty
    XBiff*emptyPixmapMask:  /usr/local/include/X11/bitmaps/mail-empty-mask
    XBiff*fullPixmap:       /usr/local/include/X11/bitmaps/mail-full
    XBiff*fullPixmapMask:   /usr/local/include/X11/bitmaps/mail-full-mask
    XBiff*shapeWindow:      true
    XBiff*flip:             false

gisli@adams.com