Pantomime 1.1.0 is required for gnumail 1.1.0. pantomime 1.1.0_pre2 is the current stable ebuild, however, gnumail 1.1.0 is stable. The two combinations will not work. Pantomime 1.1.0 is required, but it's unstable. Perhaps the two ebuilds should be synced up somehow.
Hmm, according to the home page of pantomime http://www.collaboration-world.com/cgi-bin/project/release.cgi?pid=3 version 1.1.0 is considered stable (as well as pantomime-1.1.1) I think, the new version 1.1.2 is also considered stable ...
newer package available