Generally when you are using Microsoft Outlook, recently used contacts come up under the AutoComplete list when you are using the To box to address a new email. At one client site recently this wasn’t happening for a few contacts – and ones they did use on a regular basis.
The solution involved going offline as you have to seem to send an email to the added contacts – click the Send/Receive tab, then in the Preferences group, click Work Offline. Now go to the relevant Contacts folder and select the required contacts by holding down the Ctrl key and clicking.
Then on the Home tab, in the Communicate group, click Email. The relevant email addresses will now show in the To box. Click Send.
Because you are offline, the message will now be in the Outbox. Go to that and delete the message. Then go back online, by going back to the Send/Receive tab and in the Preferences group, clicking Work Offline again.
Next time you try to send an email, the required contacts should be in the AutoComplete list.