|Outlook can't suggest contacts until it "knows" about them. It doesn't search or scan the contacts list, it learns about a new contact when it's used. You can prove this by sending an email to a contact and then the next time you start typing the same address, it'll pop-up.|
To make Outlook "aware" of all your contacts, just...
1. Create a new e-mail message
2. Click the "To" button
3. Select ALL the contacts in the list as though you are sending an email to every one in your address book.
4. Click the "To" button at the bottom of the list and click the "OK" button. You should now be looking at a new email with all your contacts listed in the "TO" field.
5. Cancel the email.
That's it. Now Outlook has "seen" every contact on the list and should now suggest names when you start to type just like before...