Dear @MARSHALL, Louise,
I hope you’re having a good day and thank you for raising this.
In New Outlook for Windows, AutoCorrect and spelling are handled a bit differently, so the change you made in Word doesn’t always carry over. Based on testing on my side, the approach below has worked well to stop this behavior.
Here’s what I’d suggest trying:
First, create a new email in New Outlook.
In the message editor toolbar, select Editor. From there, open Editor settings.

Within Editor settings, disable Auto corect:

After updating these settings, it’s important to fully exit Outlook so the editor state is refreshed. Please make sure you:
Close all Outlook windows
Right‑click the Outlook icon in the system tray and choose Quit
Then reopen Outlook and test again by typing “Greta” in a new email
After doing this on my side, Outlook no longer automatically replaced the name during typing.

If you still see the same behavior after these steps, please let me know. That will help confirm whether this is a limitation of the current New Outlook editor in your environment, and I’ll be happy to look at further options with you.
Thanks again for reaching out, and I hope this helps improve the writing experience for you.
Warm regards,
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