Exporting Folders from Thunderbird
Thunderbird does not provide native support for exporting more that one email to other programs at a time. To do this we need an add-on. ImportExportTools (Mbox enhanced) 18.104.22.168 offers support for exporting a Local Folder and all of its emails to a variety of formats. The file we need can be found here. The download link is at the bottom of that page.
Installing the Add-On
Once you have downloaded the file, open Thunderbird. Under the Tools menu at the top of the window is a selection for Add-Ons. When you select it the following screen will appear:
Make sure you have selected the Extensions tab at the top before clicking the Install button. Clicking Install will allow you to browse to the location you downloaded the Add-On file to. Select ImportExportTools-22.214.171.124.xpi and Open it. On the next screen that comes up, wait for the option to "Install" to activate, and click it. The window will close and bring you back to the Add-Ons window, now with a button to restart Thunderbird pictured below.
Once Thunderbird restarts, the Add-On will be installed and ready to use.
The ImportExportTools Add-On adds itself to the context menu when you right-click on a folder in Thunderbird's folder listing. By mousing over its entry, another menu appears with options specific to ImportExportTools.
To bulk export mail, select the folder you wish to export from, right click on it and select Import/Export -> Export all messages in the folder, then select the format you would like to save your emails in. The standard Windows "Browse for Folder" window comes up for you to indicate where you want to export your emails to. The emails will actually be saved in a folder inside the folder you select, complete with an index, unless you are exporting as a spreadsheet.
EML format is for if you would like to open the emails in another email client, such as Outlook. HTML format will allow you to view your emails as separate web pages. Plain text format will allow you to open only the text of the emails, without attachments, images, or other embedded media in a word processor. The Add-On gives the option to append all of the emails to a single file, or to split them up into one file for each email in Plain text format. Exporting as a spreadsheet creates a spreadsheet with one email per row, and split into columns for subject, sending address, receiving address, Date/Time, and the first line of the email if it is text.