mail-filter/amavisd-new saw the introduction of the dkim USE flag, but as of 2.6.3-r1 it unconditionally depends on >=dev-perl/Mail-DKIM-0.31. I'm not sure if it is really required by the code even if not in use, but maybe it could be depended on only when USE=dkim ?
*amavisd-new-2.6.3-r1 (08 May 2009) 08 May 2009; Tobias Scherbaum <dertobi123@gentoo.org> -amavisd-new-2.6.3.ebuild, +amavisd-new-2.6.3-r1.ebuild: Fix dep on dev-perl/Mail-DKIM, it's needed even when no dkim funtionality is activated. #268928
(In reply to comment #0) > I'm not sure if it is really required by the code even if not in use. It is.