I have done this multiple times in the past (I have several files - not folders - that contain mail). However due to the fact that II was somewhat brain damaged several years ago I can no longer remember (or figure out) how to do it. For instance, I have a "MoreJunque" mailbox file that is (from the "Properties" dialog) at mailbox:///C:/Users/Daniel Mathews/AppData/Roaming/Thunderbird/Profiles/bxk6ngnt.default/Mail/pop.att.yahoo.com/MoreJunque. However, my inbox is in mailbox:///C:/Users/Daniel Mathews/AppData/Roaming/Thunderbird/Profiles/bxk6ngnt.default/Mail/pop.att.yahoo.com/Inbox. These are unique files that contain folders.