The recipient list is a pretty poor way to deal with things when you
get mail sent to multiple lists you're on, and often the To: line ends
up with nothing at all.
I filter on envelope recipient. This seems to work very well,
although it does cause problems with certain obnoxious lists and
list-manager programs (I won't mention any names) which are unable or
unwilling to deal with people sending mail using a different address
from the one they receive it at. It also lets my MTA do all the work
of sorting things for me.
I do the same thing, and it works extremely well for me also.
FWIW, my bulk_mailer code has a fuzzy address matching algorithm that
is designed to recognize when the sender of a message is using a
similar-but-somewhat-different address (via subaddresses or slightly
different domains) than the one to which he/she is subscribed.
Authors of other list software are welcome to crib from it.
Keith