The hypermail package is one approach:
http://www.eit.com/software/hypermail/hypermail.html
It takes mailbox files and turns them into hypertext archives,
with index files by Subject:, author(From:), Date:, and thread.
It seems to use In-Reply-To: and Reference: where available and useful,
but not anything from Subject:/Date: for the thread index.
I feel hypermail is a good start, but lacks some features -
preserving all headers, a more effective threading algorithm,
more tunable hyperlinking, and some capability for links
or indexes by keystrings. Also, as the pure volume of posts
grows, a brute force hyper-index becomes more unwieldy.
Still, hypermail could be useful for the situation of
"questions asked more than rarely, but less than frequently,"
that can often arise on a list as new members join over time.
A result for a lower volume list (~15MB over 8 months) is at:
-- Denis McKeon dmckeon@swcp.com