NewOutlook · Desktop · Web
Outlook: Spell check before sending emails in new Outlook
New spell check feature will be available in Outlook allowing automatic spelling verification before email sending. This is an optional capability for users who want to avoid sending messages with spelling errors.
Microsoft's description
If you don’t want to check spelling manually for every message—or you’re worried you might forget!—you can set Outlook to check spelling for you every time before sending emails.