mboxPack Description:

mboxPack - Pack individual email files into mbox files. - A quick, simple and easy to use utility that lets you combine eml, msg and txt email files into Thunderbird compatible mbox files that are ready to use! Got old email that you want to get into Thunderbird? This utility makes it easy!
Functions
Provides an easy to use utility that will scan a location for individual email files, and pack them into mbox files that are compatible with many email programs like Thunderbird. It will test each file found in your specified input folder (and recursively below) to make certain that they are valid email files, and then pack them into standard mbox files. Each input folder of msg, eml or txt message files, becomes a like named mbox file in your specified output folder.

Features
Windows compatibility
Speed
Reads Paths Recursively
Confirms files found are valid email before adding them to the mboxes
Groups the email based on folders that they were found in and names the mboxes the same as those folders
Allows you to select the input folder
Allows you to select the output folder
Allows you to open the input folder directly from the menu
Allows you to open the output folder directly from the menu
Creates .sbd folders
Output is ready to be 'dragged and dropped' into your Thunderbird mail folder