It happens to everyone: the email with the directions or the exam information you're certain you saves is suddenly missing. When you find missing e-mail folders in your Thunderbird account, don't panic. Mozilla, Thunderbird's manufacturer, offers several search strategies for recovering missing e-mail folders. Try the strategies one at a time until you see your e-mails restored. Getting the email back may take time, but as long as you haven't compressed the email folder, you will get the messages restored.
Select "View" from Thunderbird menu options. Click on "Messages" and make sure it's set to "All." Then click on "Threads" and make sure this is set to "All," too. This can affect missing e-mail folders.
Click on "Folder" then "Advanced Folder Views." This should be set to "All Folders." If it was not, switching it back to "All Folders" should cause your folders to reappear.
Check "Junk" and "Trash" folders in case you accidentally removed the email folder to your trash. If you find it there, click on it and drag it back into your inbox to recover those e-mails.
Quit Thunderbird and restart it to see if the email folders reappear.
Restore the folder index if you have the email folder but it is empty. To do this, right-click on the folder and hit "Properties" then select "Rebuild Index," which is under "General Information."
Search your PC for the missing folder using the search function. For example, if the missing folder is called "Client Emails," type that term in the search box. Look for the result that has no extension--"Client Emails" rather than "client-emails.msf" where ".msf" is the Thunderbird Extension. Then open the "Client Emails" using a simple text editor and look for the phrase "X-Mozilla-Status" with numbers after it. Change the numbers to "0" then save the file. Drag the "client-emails.msf" to your Recycle Bin to rebuild the message index with your changes. Then quit Thunderbird and restart. You should see your folder with the messages.