How to remove an invalid email from your suggested lists

Microsoft Outlook maintains a list of suggested contacts that is used by the automatic name checking feature and the automatic completion feature. Over time, the list of "shortcuts" of commonly used e-mails in your nickname cache will automatically grow; this can be a very useful tool. The downside to this feature, however, is that your nickname list will sometimes contain an old or invalid email address (e.g. for users who have changed their e-mail address or who have modified their account settings). When you use one of these outdated nicknames, your messages may fail to send, or they may not get to the desired recipient.