My school uses
FirstClass for email and other collaboration things. I know a lot of private schools and some businesses use it for collaboration, and I imaging some Gentoo users would like an ebuild for it, so I wrote one and submitted it as
Bug #148817 on Bugzilla. If you use FirstClass, please put the ebuild in your Portage overlay and see if it works. I've marked it x86, not ~x86, so it should install without unmasking.