how to delete "no recipent no sender" messages

Help! Recently, I began to get messages in my Inbox with no content marked "no recipient, no sender" with no way to delete or move them. Sometimes going back to my mailboxes and the returning to the Inbox would get rid of them but not always. Now, I have the same type of message in my Sent mailbox...around twenty of them! Does anyone know what the glitch is that is creating these weird messages and, more importantly, how to delete them?

Thanks in advance!