Hi,
Could you please provide more details about your issue by answering the following questions?
- Are you getting this error in Outlook? How about OWA?For Outlook client, you could try to use SARA. Support and Recovery Assistant is a new tool that helps users troubleshoot and fix issues with various Office 365 apps and services. The app diagnoses common Outlook issues like account setup, connectivity issues, password issues, or Outlook stops responding or crashes. https://support.office.com/en-us/article/about-the-microsoft-support-and-recovery-assistant-e90bb691-c2a7-4697-a94f-88836856c72f?ui=en-US&rs=en-US&ad=US#/?env=ExRCA
- Is this the only user in the organization having the problem?
- Is the mail from shared mailbox?
- Does this issue occur when this user logs in on another device? It's suggested that you could provide a screenshot of the error. (In order to avoid the privacy leakage, please remember to hide your personal information.)