Hello TedPES!
I'm Gema and it's important to me to ensure that all your questions are answered and that you have a positive experience.
I advise you to analyze if the address that is appearing is the real one.
Could be Spoofing. A type of program that masks an email address and is used to hide the sender's real location.
If you right click on the message and select View -> View message source, a technical report of the message will be displayed. By using the function to search the document (CTRL + F) and search by Return-Path, the real sender will be located.
If that's not the case, there's no need to worry.
If you want more details, please note the information in the documentation https://support.microsoft.com/en-us/office/bloc...
And if you still have any questions, please reply with the details to help you out.
Thanks for using the Community