It looks like IMP has been imported into the FreeBSD ports tree:
http://www.freebsd.org/cgi/cvsweb.cgi/ports/mail/imp/
It should ship with FreeBSD 4.4.
--
Jon Parise (jon@csh.rit.edu) . Rochester Inst. of Technology
http://www.csh.rit.edu/~jon/ : Computer Science House Member