Hi Fung(2),
First of all, thank you for your reply, I am regret that you marked my reply as not helpful, because I am doing my best to help you solve the problem. And I want to confirm with you again, have you tried to change the browser and use the privacy mode of the browser?
Secondly, I want to make it clear to you, Community is a place for everyone to exchange problems. And as Community Support, we have the same permissions as users. I'm sorry that I don't have enough permissions to perform any checks on the mailbox server. And I also provide all the solutions that are within my permission to provide.
I see you tried to contact Outlook.com support, but were unsuccessful, please make sure you sign in with your personal Microsoft account, not your work and school account and contact Outlook.com online support staff during business hours.
I hope this information was helpful. If you have any questions, please let me know, I will be happy to help you further.
Have a good day.
Best regards
Jim - MSFT | Microsoft Community Support Specialist