Also introduced in Thunderbird 38 (38.0.1) was the ability to use Maildir mailbox format. Like OAuth2, this too has not been very well documented. I have no idea what this does or why you would want to use it. Further, I have not tried it, especially after I found this information on the Mozilla Wiki with the warning about enabling said feature: Though, we aren’t sure of the side-effects of using maildir as the default store on a profile that was created on Berkeley mailbox(mbox) format; so we suggest you to create a fresh profile to work with maildir so as to avoid…