Lysozyme talks about bloglines providing email to rss feeds along with mailbucket. Bloglines is handy if you’ve already got an account with them, but mailbucket is better as you can just think up an email address @mailbucket.org when you want to create an rss feed for a newsletter. The only problem with this sort of thing is if everyone decides to subscribe to Langalist (for example) then there could be several rss feeds at mailbucket.org all for the same newsletter. The disadvantage is also that the list is public, so anyone could unsubscribe the feed, whereas at bloglines it is under your control.