managing contact list and e-mail addresses

I want to delete people from my contacts list - and it looks like I have done by going into 'People' and looking alphabetically...there is only one (the latest) e-mail address for my friend.. Yet when I write an e-mail and put in the first initials for the name, all the deleted versions come up as well and I have to take care to choose the right one. How do I stop these unwanted and out of date addresses coming up when I want to send an e-mail. I have spent ages trying to sort this.