Update Your Copy of the Global Address List (GAL) in Outlook 2007
STEP 1: Open Outlook.
STEP 2: Click on Tools -> Send/Receive -> Download Address Book.
STEP 3: Uncheck the box next to Download changes since last Send/Receive. In the Information to Download section, select Full Details and in the Address Book section, choose Global Address List. Now click OK.
STEP 4: The new version of the Global Address List will now be downloaded. A status window will open to indicate that the download is in progress and will close automatically when the download is complete.
After a new version of the Global Address List has been downloaded, you should be able to send to all recipients.