1. I need to ensure if this issue is related to the service upgrade. Has the service upgrade of your Office 365 tenant been completed?
I think so, how can I check to be sure/
2. Does this issue happen recently? How long has it lasted? Do you mean this issue occurs after the upgrade?
The Issue started yesterday.
3. Since the emails cannot be pushed in Outlook for Mac client, if you manually click the send/receive button, will the emails be received?
If i manually click the send/receive button mail does come through.
4. Moreover, please have this affected user use Outlook Web App (OWA) to receive emails, is OWA working well?
No other user is reporting a problem, OWA works fine, I tested this user on Outlook 2010 for Windows and had no problems.