Sending, receiving, and organizing email in Outlook on the web for business
Dear Wu Jian,
I'm sorry you've been unable to send or receive emails since yesterday. If your issue is urgent and you would like to contact support by phone, you can visit this official page: Customer service phone numbers - Microsoft Support. The support team will assist you as soon as possible.
If you can reach Microsoft by phone, use the official Global Customer Service phone numbers list. Choose your region > your country > if your country lines fail or lack English support, select a nearby country (e.g., Singapore) or the United States number, Microsoft explicitly allows this.
In addition, could you please let me know what error you see when you try to access your email? Have you already contacted your IT admin to check this, or are you the admin of your organization?
Thank you very much for your valuable time and your cooperation. Looking forward to your response.