Using New Outlook on Windows for personal email, calendar, and contact management
Hello Steve,
Thank you for reaching out.
I understand that you are having issues opening encrypted emails. Please let me know of the following to better assist. Thanks in advance.
May I please verify the type of account you are using? Is it an M365 work/school account or a Microsoft/personal account like Hotmail/outlook.com?
->Also, after getting the one-time passcode, are you getting any errors when trying to open the email? If so, please share with me the error message that you are getting as this might provide more information about your situation.
You can also try to open these emails with your main account instead of your alias and check if this is successful. How do I open a protected message? - Microsoft Support
Kindly note that this above requested information is required for further analysis and troubleshooting of your situation. Your patience and cooperation are much appreciated.
Looking forward for your response.
Best Regards,
Ashraf.