When changes are made to the internal Offline Address Book—specifically those that are related to email address changes, mailbox updates, and other "system" changes—Outlook does not always update the local copy of the Offline Address Book.

Directions

This process may take some time to complete. Please allow up to 15 minutes for the address book to update completely.

Open Microsoft Outlook.
Select the Send / Receive tab.
Click Send/Receive Groups and select Download Address Book.

If you do not have the Download Address Book option, you are working in Online Mode and do not need to update the Offline Address Book.
Make sure that "\Offline Global Address List" is selected and then click OK.

If updates are missing, uncheck Download changes since last Send/Receive.

Troubleshooting

If the Offline Address Book successfully updated, but you are still unable to send to a particular email address, you will need to remove the type-ahead (or auto-fill) entry from Outlook.

Open Outlook.
Create a new message.
In the To field, type the first few letters of the affected address.
Click the X next to the affected address to remove it from your type-ahead list.

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