Current stable in portage is 0.36 (06/2009), current stable upstream is 0.38 (03/2010), which fixes some bugs and does not introduce any incompatibility with previous versions. 0.38 is already in portage, please stable that and drop older releases if there isn't any reason to keep them around.
dev-perl/Mail-DKIM-0.38 emerges correctly on my Gentoo/HPPA with FEATURES=test I upgraded my systems from -0.37 (was ~hppa, worked very well since 11/2009) and it seems to be doing its job.
additionally: * no open bugs * in tree since 07.04.2010
amd64 stable
Stable for HPPA.
ppc stable
alpha/sparc/x86 stable, ia64 will pass
ppc64 stable