Turn on automatic spell check

1. In classic Outlook, go to File and select Options.

2. On the Mail tab, select Always check spelling before sending in the Compose messages group.

3. Select OK.

By default, new Outlook checks spelling and grammar.

1. To modify Editor settings, in a new email message, on the Options tab, select Editor > Editor Settings.

2. Under Corrections, you can turn Spelling or Grammar checking on or off. You can also expand either category by clicking the adjacent > symbol and then selecting which kinds of specific spelling or grammar checks you want performed automatically. 

3. Select OK when you're done. 

By default, Outlook for Mac checks spelling and grammar.

1. To modify Editor settings, in a new email message, go to Outlook > Settings and select Spelling & Grammar.

2. You can turn Spelling or Grammar on or off. You can also select a writing style under Grammar Settings or expand the Grammar category by clicking Settings and then selecting which kinds of specific spelling or grammar checks you want performed automatically. 

3. Close the window when you're done.