[SOLVED] - Unable to Delete Messages in Thunderbird Email Client

If you cannot delete messages in Thunderbird, it may be caused by a corrupted trash folder.

Here is how to delete the corrupted trash folder and create a new one:

1. First, open your Profile folder:
    
• At the top right of the Thunderbird window, click the menu button 
  
  New Fx Menu , then select Help, and then Troubleshooting Information. The Troubleshooting Information tab will open.
  
• Under the Application Basics section, click on Open Directory. A window with your profile files will open.
  
2. Close Thunderbird.
    
3. Open the Mail (or ImapMail) folder in your file manager (according to whether you are using POP or IMAP with the affected account).
    
4. Open the folder with your incoming mail server name (something like imap.googlemail.com or pop.googlemail.com).
    
5. Select the Trash and Trash.msf files and delete them. In some accounts, these may be named Bin or Deleted.
    
6. Restart Thunderbird.
    
• If you are using IMAP, a new Trash folder will be automatically created by Thunderbird.
  
• If you are using POP:
   
1. In the folder list, right-click on your account name and select New Folder....
    
2. Enter Trash as folder's name and confirm by clicking on Create Folder.

The trash will reappear and you will be able to delete mail again.

Source: https://support.mozilla.org/en-US/kb/cannot-delete-messages