j: Next unread message
k: Previous unread message
j a: Jump to all threads
j l: Jump to MailingList overview
N.B. This is off-topic. If you really care that much, people who want to hear about it are over on email@example.com.
Cameron Simpson writes:
There isn't one, can't be one at present, and likely won't be one in the future: http://www.jwz.org/doc/content-length.html. This still applies to some extent today despite Jamie's rant being almost 20 years old -- Mailman can't choose the mbox spec being used, that depends on the MTA.
If you want something that could actually have a MIME-Type, there's Babyl, MMDF, or (file-per-message) maildir, all of which have reasonably precise specs -- but aren't in anywhere near as wide use.
Maildir is what Mailman 3's bundled "trivial archiver" uses, as it's far more robust and easier to handle than mbox.
I still content that any change that removes the simple ability to fetch the list archive for use by the end user is a huge step backwards, regardless of the prettiness of whatever replaces it.
It's not a question of "removing". This has always been a user choice, and many lists use third-party services (mail-archive.com) or non-pipermail archivers (MHonArc). It's just that Mailman 2 with its bundled mbox-format archiver made it easy to provide by default.
If lots of users really prefer pipermail, for whatever reason, it's not that hard to add by hand, and could be packaged on PyPI.