When you start to address a message, Outlook displays a list of suggested contacts. These contacts are from your Outlook contacts, your organization's offline address book, and also from your recent addresses list. The recent addresses are addresses that you have recently sent a message to or received a message from.
In a new e-mail message, start to type a name or address in the To, Cc, or Bcc box.
A list of suggested contacts appears.
Under the heading Contacts and Recent Addresses, click the x next to the recent address that you want to remove.
Note: Contacts that you have saved in Outlook or contacts from your organization's directory can't be deleted from the recent addresses list.