I know you have been using Hotmail for a long time. Was there a time when you set up a group to use for sending emails? I am thinking that there could be a few folks who are hard coded into the group and are no longer in your contact list. I am just guessing that it might be possible that when you delete someone from your contact list that Outlook removes them from your group address as well - but that it hasn't always been so. The result would be some names exist only in your group address list and not in your contact list so to delete them you would have to open the group list and remove them.

All speculation on my part - hopefully someone who knows something for sure will come along and provide you some real help...