I've built and run successfully msmtp-1.4.4, using msmtp-1.4.4.ebuild.
how about msmtp-1.4.4-r1?
It is in package.mask like all the others mta that use the mailer class, but in this contest it does change nothing.
ah, my bad. Sorry about that. Which USE flags have you used? mailwrapper needs net-mail/mailwrapper-0.2.1 to be keyworded first.
/me keyworded mailwrapper && msmtp.