If you've ever typed a misspelled email address in the To or CC fields of an Outlook message, a problem occurs because Outlook will remember that bad address. Because Outlook has an auto-complete function, so every time you begin typing an address any incorrect ones will also appear in the auto complete list Outlook offers you.
Fortunately there's an easy way to clear any misspelled (or out of date) email addresses:
- Start typing the incorrect address so it appears in the To field
- Press the down arrow key to select the auto completed address
- Press the delete key to remove the address from Outlook's address cache
Note: this trick also works in other applications, like Firefox. Give it a try!