The spellchecker in Outlook tells you their names are not in the dictionary and recommends an alternate spelling. To add, edit, or change words in your (ever expanding) custom dictionary:

• From the Outlook toolbar, Tools | Options | Spelling tab.
• Click the Edit button. (You may receive a warning message that says any changes you make will not be reflected in open messages. If you do, click OK to continue.)
• In the resulting Notepad document, type any new words you want to add. Press Enter after each word, so only one word appears per line.
• When you’re finished, click File, then Save, and exit the document.