I wrote a mailing list archive thing for the css-discuss list in PHP a few years ago, but the source was never released. It took the best part of 12 hours - they really aren't very complicated pieces of software. In Python it would be even easier thanks not only to the email module but also to AMK's threading module: http://www.amk.ca/python/code/jwz
For search, I'm a huge fan of http://www.swish-e.org . It has good Python bindings (if you hunt around a bit) and its easy to set it up to index pretty much anything. I used it for the search engines on http://www.ljworld.com and http://www.lawrence.com .