i have a perlfilter script (virus scanner via amavis) running on two
mailservers and i was unable to make perlfilters work other than with the
perlfilter-mode set to "all" (file etc/filters/perlfilter-mode). the
symptoms were as you described and up to now i do not have a solution for
that problem (which for me isn't a problem any more because i want all mail
going through my servers to be scanned anyway).
that's weird. when I do this, I can no longer send mail.. it gives me
an error of "A password transition is required" - whatever that means.