After using Thunderbird for several years I noticed my backup of it kept increasing. It had always seemed bigger than it should be as I only keep a few emails archived in it. Eventually I saw an extension called XPunge which stated that Thunderbird does not delete your emails (even if you empty the Trash folder) unless you compress the folders (which is what that extension does by clicking on the button they provide). This made me realize that this was why my email backup was becoming so big. So as long as you donâ€™t use the compress folder option in Thunderbird, you have the ability to restore your deleted email, including the attachments.
Go into Thunderbirdâ€™s profile folder then inside the Mail folder. Now depending on how many email address you have setup in Thunderbird it could be in several folders, but it will be named with either Local Folders or with the POP address you are using. (You can find out easily by going to Tools >> Account Settings and then going under the account you want to restore email address for and look under its Server Settings and at the bottom look at the path for Local directory). Iâ€™d recommend closing Thunderbird once you know where to go. Make a backup of the file called Inbox (Note: itâ€™s the one with out an extension, Inbox.msf is for something else). Now open up Inbox in your favorite Text Editor (Notepad, Crimson Editor, Notepad++, etc.), it may take a few minutes to load depending on how big the file is, some of mine were over 90MB. Donâ€™t open it in WordPad, since it will add formatting to the file, also keep in mind Notepad on Windows 98 has a file size limit and wonâ€™t handle really huge files. Now you can search for whatever emails you are looking to restore, or have fun looking at really old emails. When you find one you want to restore, scroll up and change number after X-Mozilla-Status: to be a 0 (zero). Itâ€™s okay to just make it a single zero rather than a four digit number. Donâ€™t bother changing the X-Mozilla-Status2. Do that for each email you want to restore. Then save the file. Open up Thunderbird and it should now be in your Inbox marked as Unread (Note: it may take awhile for it to read that Inbox).