Hello Ned,
Thanks for your feedback. I agree with you that the lists in address/envelope/header are not-necessary-expandable (could be very large or only check for membership can be made). However this thoughts are not valid for "reject :list", where the parameter has to be a necessary-expandable list.
Actually, that's not the case. One way to implement redirect :list is to look up the list name and turn it into a list address, then send to that address and have the expansion occur completely outside the Sieve context. This approach probably doesn't make sense for a Sieve implementation operating before final delivery, because in that case the implementation should not have problems accesing mailing list content. But an MUA-based implemenation accessing service-side lists might be required to operate in this fashion. The content of mailing lists can be sensitive. Ned