restore continually populates itself with a message sent long ago. It does this multiple times until all available memory is used up. I must clean out the root file in "library/mail/mailboxes/restore"

Restore mailbox in Mac mail app continually populates itself with a message sent long ago even though I empty the mailbox. It will backup the message over and over until all available disk space is taken up. I then have to go into the system to send the files stored in the "restore" mailbox to trash. I do not know how to prevent "restore" from trying to backup the same message ad infinitum.