I would start by looking where a function named "effective_t" is being called in the entire program, including the Mail::Audit module. It may not be obvious, so be thorough - for example, $obj->$func() may be doing it because $func is set based on some mail header or something. If that becomes difficult, perhaps overload AUTOLOAD yourself, and anytime $AUTOLOAD is set to /::effective_t/, croak (with stack traceback). Otherwise, set your parent's $AUTOLOAD, unshift $self back onto @_, and then goto &SUPER::AUTOLOAD (or something like that). It's a bit tricky, but the point is to insert a traceback which may help narrow down where effective_t is being called from.

Good luck!