RECOVER DELETED MESSAGES: an extension that allows to recover deleted messages, if the folder has not been compacted yet. To use it, select the folder, right-click and choose "Recover deleted messages", then follow the messages in status bar. From the 0.2 version it should be able also to recover deleted messages from Imap folders, if they're set for offline use.

https://freeshell.de//~kaosmos/index-en.html#recDelMsg

Thank you! I'm new at computers so I do not know what an extension is, or what right click means. Also what folder? Thanks again for your kind help, John