Yes, it happens to us all at one point or another, I suppose! Anyway, during the last update, I had a total of 97 e-mails that were returned for various reasons, by far the most common was the "Mailbox unavailable" excuse given by Hotmail. Other addresses were just not recognized. So, follow the "Bad e-mail addresses" link to the right and make sure you're not listed. If you see the name of someone you know and you can get in touch with them, let them know they need to update their e-mail address here. Thanks!