Using the spell check you can review your message for spelling mistakes. If a word is not matched in the database, the page displays a list of words that are the suggested spelling. Choose a highlighted word that is spelt incorrectly, and a menu will appear with suggestions.
If a word is spelt correctly, and the page throws a spelling mistake, click 'Add Personal' for the word to be added to your own personal dictionary.
Once you have finished spell-checking click the resume button to return to editing the email.