Hi Merch,
From your description these sound like spam emails. Just delete.
From the web:
E-mail users are receiving an increasing number of bounceback spam, known as backscatter. The bounceback e-mail messages come in at a trickle, maybe one or two every hour. The subject lines are usually, but not always: 'Cyalis, Vyagra nad Levytar,' 'UNSOLICITED BULK EMAIL', apparently from you. Bounceback messages come from legitimate e-mail servers that have been fooled by the spammers.
You can also ensure Outlook only sends when you tell it to, and not on connect or when pressing Send in your actual email.
If you are getting lots and lots of these, you may need to reset your password, as it could indicate a compromised account. If you are worried, contact your ISP.
PS. Do you have any other email accounts?; Hotmail. Gmail? are these OK?