One of the most frustrating issues to deal with in Outlook is having an email history file that is either too large, or full of incomplete/incorrect email addresses (specially with lifetouch employees). When you begin to type an email address in the TO: field, Outlook looks into the history cache and creates a dropdown list of email addresses, contacts or exchange names to match. It holds the last 1000 used addresses. New names are not added until the current outlook session ends and outlook is restarted.