Thank you for posting your question in the Microsoft Q&A forum.
To help us investigate this issue more accurately, could you please provide the following additional information:
Does this behavior affect other accounts in your company, or only your account?
Have there been any recent changes?
When sending emails, do you see any error codes, or does the sender receive any NDR/bounceback messages when emailing your account?
In the meantime, you can also contact your tenant administrator to check and verify your account configuration to ensure there are no licensing issues and that your account is fully available for use.
Please also check if Outlook is currently in “Work Offline” mode:
Open Outlook.
Go to Send/Receive.
If the Work Offline button is enabled, click it to turn it off.
Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution.
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