Whenever you delete a message in JoMail, it goes into the Trash folder. The trash folder can act as a safety net if there is something that you deleted accidentaly. If you decide that all the messages in your trash folder are in fact trash, then feel free to delete away. To delete mail messages in the trash folder click on File -> Empty Trash.
The trash folder is a folder like
any other. You can delete messages from the trash folder and they will
go away. This is another way that you can empty the trash folder. Select
all the message in the folder by using the Ctrl key or Shift
key, then press the Delete key.