The module in pre-release state. It started as patch to the mailarchive module on Nov/11/2007 - At that time I was not aware that Jeremy - the author of the mailarchive module - has been working on a sphinxsearch version. So instead of releasing it as a patch I've revamped my code as module that depends on the mailarchive module.
It works pretty well, yet still has the rough edges of quick pragmatic development.
After enabling the module you'll find a “Mailarchive Serach Settings” in the System configuration menu (enable indexing there) and a “Mail Archive” tab will appear on Drupal's search page.
Searching won't work until there's a swish-e index file. The swish-e index is (re-)built automatically (via cron - see your
admin/logs/status page) when it's nonexistent or older than the latest message in the mailarchive.