If your grammar detector is not working as expected in Outlook, check your settings. You can see all options for on/off in Microsoft Office here.
Here's how to do that:
- In Outlook, go to Options > Mail > Spelling and auto-correct > Proofing
- Make sure that, at the very least, the 'Grammar with spelling' box is ticked and the 'Grammar & Style' is also selected in the drop down menu (yours may just be on 'Grammar')
The grammar detector in Credosity for Outlook should then work as you'd expect.
Here's more from Microsoft on how to customise the grammar, spelling and style features in Word and Outlook. Keep in mind this varies slightly from one version of Office to the next. If you're on Office 2016 there are less grammar/style features than previous versions. Fear not - they have improvements planned.