Before you send a message, Microsoft Outlook automatically checks the names you type in the To, Cc, and Bcc boxes (To, Cc, and Bcc boxes: A message is sent to the recipients in the To box. Recipients in the Cc (carbon copy) and Bcc (blind carbon copy) boxes also get the message; however, the names of the recipients in the Bcc box aren't visible to other recipients.) against the names in the Address Book and against those contact folders that you've specified as Outlook Address Books. If an exact match is found, the name is underlined. If multiple matches are found, a red, wavy line appears under the name. Right-click the name to see the matches.
If multiple matches are found, and you have used the address before, the name you chose previously is displayed in the box with a green, dashed underline to remind you that there are other matches. Right-click the name to see the matches.
You can also manually check names in messages by clicking the Check Names button
on the message toolbar.