In new Outlook for Mac, sentence capitalization is controlled by the Editor autocorrect settings.
To turn automatic capitalization back on when composing a message:
- Start a new email or reply to an existing one.
- On the message ribbon, select Editor.
- Choose Editor Settings.
- Use the toggle to turn autocorrect and auto capitalization on.
If using classic Outlook for Mac instead of the new experience, autocorrect is managed via Outlook Preferences:
- On the Outlook menu, select Preferences > AutoCorrect.
- Make sure Replace text as you type is selected.
In Outlook on the web (if composing there), the same Editor Settings panel is available on the ribbon of a new message under Editor > Editor Settings, where autocorrect and auto capitalization can be toggled on.
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