Howto export a mailing list thread to HTML or plain text. Thread have 40+ mails. I use OS X if that matters.
export should be well formatted and readable
The ImportExportTools add-on can export all messages in a folder as a single text file, a series of html files with an html index, or a series of individual files (.eml, .txt, html). Works well on Windows, don't know about Mac.
Found by way of the related Export list of mails in Thunderbird