[Exim] Mail List Software Suggestions

I've been using majordomo for some lists and would like to upgrade to
something better - and I'm looking for suggestions as to what people
consider the "best" mass mailing software.

Among other things - I work for a not for profit org (Electronic
Frontier Foundation) and we send a newsletter to about 20,000 people. Of
course - whatever solution needs to work well with exim.

What I would like is if the mail list software could personalize each
message inserting the email into the "to" field ans if each message was
for the recipient only.

Also - we have a lot of small lists and I'd like something that was easy
to manage as far as adding and deleting users.

So --- what do you all like?