Exchange Server not syncing emails to Outlook clients properly

Hi @Holmes Shanquaneta

Thank you for posting your question in the Q&A Forum. 

I understand how frustrating it can be when Outlook desktop clients are not syncing properly even though Outlook on the web works fine. This suggests that the mailbox itself is healthy, but there may be an issue with how the Outlook client connects to the Exchange server. 

As a moderator, I don’t have access to your specific server environment, however, I can guide you through some standard diagnostic steps. 

To help narrow down the cause, you can run the following diagnostic checks in Exchange Management Shell (not standard PowerShell). These commands will not fix the issue directly, but they will give us important information about server connectivity and certificates: 

# Test mailbox connectivity 
Test-MAPIConnectivity -Identity ******@domain.com 
  
# Check Exchange certificates 
Get-ExchangeCertificate | fl Subject,Thumbprint,NotAfter,Services 
 

Please replace ******@domain.com with one of the affected mailboxes and mask any sensitive information before sharing the results. 

You may also run the Outlook Connectivity test via Microsoft’s official tool: Microsoft Remote Connectivity Analyzer 

To help us investigate further, please share the following information to help us understand the issue better: 

• The exact error message or status that appears in Outlook desktop when the problem occurs, for example ‘Disconnected’, ‘Need password’, or ‘Cannot connect to server’. 
• Any client-side troubleshooting already attempted, such as creating a new Outlook profile, clearing or rebuilding the OST file, or running Outlook in Safe Mode, and the outcome of each step, whether the issue was resolved or persists. 

After running the diagnostic commands above and completing the client-side steps, sharing these results and details will help determine the next steps together. 

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".    

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.