The mailarchive module allows you to subscribe to one or more mailing lists, messages from which will be stored in a threaded archive. It is then possible for users to browse and search these archives.
Active development is only happening in the 6.x branch of the code. Bug fixes will be accepted for the 5.x branch, however it is no longer being actively developed or maintained.
6.x-2.x-dev requires MongoDB. 6.x-1.x-dev does not.