Although it is not complete browsing maildirs, indexes, and messages now works well enough that I'd be curious if there is any interest.

https://github.com/skx/lumail/ http://lumail.org/

Now that the initial challenges are handled the next step is to wire up more primitives for the lua-scripting, implement "compose", "reply" and view/save attachments.

Then it will be my main mail client.