Because you are using autocompletion, not autoresolution. Only the latter
uses your Contacts. The former uses a cache of names from previously sent
messages.
Use autoresolution (Check names) if you want to search your Contacts.

Signature
Russ Valentine
[MVP-Outlook]
> When I get an e-mail, right click on the from and add to contact, how come
> it will not automatically find that e-mail address when I send a new
> message and start typing their name or e-mail address. Is there a way to
> fix this.