You may have seen this in your inbox on the odd occasion.
This "email" is part of the internal format of your mail folder, and is not a real message. It is created automatically by the mail system software. You can delete it, but important folder data will be lost, and re-created again with original values.
So why is it there?
Using an IMAP client (ie, webmail) and a POP client can lead to this message being generated in your mailbox.
The message is automatically created by IMAP clients for internal record keeping and is not displayed by most email clients.
