Outlook can suggest words or phrases as you compose messages.
Accept suggested text
If you’re typing and suggested text appears that you want to accept, do one of the following:
Press the Tab key
Press the Right arrow key
Ignore suggested text
If you’re typing and suggested text appears that you don’t want to accept, just keep typing what you intended to write and the suggestion will disappear.
Turn off text predictions
While you're writing an email message, go to File > Options.
Clear the Show text predictions while typing check box.
At the top of the page, select Settings > View all Outlook settings > Mail > Compose and reply.
Under Text predictions, clear the Suggest words or phrases as I type check box.