Mailman comes with a built-in web-based archiver called Pipermail, although it can be configured to use external, third party archivers.
Note that senders can control whether their own posts are
    archived, on an individual per-message basis.  If the posted
    message has a X-No-Archive: header (regardless of
    value), or a X-Archive: header with a value of
    No (case insensitive), then the message will not be
    archived, although it will be treated as normal in all other
    ways.