Mailman

Mailman is GNU's popular mailing list software.

Mailman lists are easy to archive: they offer the whole archive in a single mbox file; sometimes you need to authenticate in order to access it. Otherwise, an alternative to downloading pipermail's HTML archives is to download the gzip archives, from which you can assemble an almost-copy of the original mbox. Wikistats' list archive downloader is a script to do so. In addition forum-dl supports downloading pipermail archives and converting them to other formats.

Mailman2 is now EOL and there are a lot of instances that are in danger of conversion to other archiving systems, resulting in breakage of a lot of URLs.