Dear @Kati Dougherty,
Based on your description, kindly try these steps:
First, check what type of account you have
In Classic Outlook > go to File > Account Settings > Account Settings
Look at the Type column for the affected account.
1> If the account type is Microsoft Exchange
You generally cannot change the display name directly in Outlook. Please contact your IT Admin to change your display name. How do I find my Microsoft 365 admin? - Microsoft Support
2> If the account type is POP3 or IMAP
In Classic Outlook, go to File > Account Settings > Account Settings
Select the account > Change
In the Your Name field, replace Katie with Kati
Click Next > Done
Restart Outlook and send yourself a test email. Change the display name that email recipients see in classic Outlook | Microsoft Support
I hope the information shared helps point you in the right direction. Please try the steps above and let me know if they work. If not, we can continue working together to narrow this down.
The first response may not always resolve the issue right away, but with your help and more details, we can work toward a solution.
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