Open the "index.html" file with an internet browser (Mozilla Firefox for example)
This file contains a dynamic table with metadata (subject, date, from ...) which will allow you to find a message.

  * The "lib" folder is used for the operation of index.html
  * The messages.json and messages.js files contain my metadata (json format) they are also useful for the functioning of index.html
  * Then there is one folder per IMAP folder containing your messages in the desired format