Check spelling before sending an e-mail
In Outlook for Windows, there is an option to always check spelling before sending an e-mail message. Outlook for Mac does not have this option; instead it checks for spelling errors as you type. Outlook uses a dashed, red underline to indicate possible spelling errors. You can also check spelling at any time by using the Spelling button.
Do any of the following:
Check spelling automatically as your type
Check spelling at anytime