For members-only lists like this one, USE_ENVELOPE_SENDER currently allows the admin to determine membership by checking either the From: header, OR the envelope sender address.
I think a more flexible alternative would be to first check the envelope sender, and then the From: header for a match. In fact, this would make sense as the default setting IMHO.
Why am I interested in this? Because I like to post to public mailing lists and newsgroups with a 'dated' address that expires after a set period of time to thwart SPAM harvesters. Obviously I can't use these one-time addresses on closed lists, but I could get around this by posting with an envelope sender address that matches my subscription address, and a 'dated' address in my From: header. The closed list would be happy, and I would be happy.
-- (TMDA (http://tmda.sourceforge.net/) (UCE intrusion prevention in Python)