Here is the software I’m currently using to turn a number of ICANN-related mailing list archives into RSS feeds. The script can deal with most common mhonarc configurations and with pipermail archives (as used by mailman). If it can’t cope with an archive you want to turn into an RSS feed, it’s relatively easy to customize. Thanks go to Wendy Seltzer and Bret Fausett for contributing code and asking the right questions.
(Note that this script works by actually walking through the list archives using HTTP. If you have direct control over an mhonarc installation’s configuration, there’s a more resource-friendly alternative.)