Outlook Classic Teams Meeting Invite not shown as HTML Format

Hi @Chan, Keith  

Thank you for posting your question in the Microsoft Q&A forum. 
We completely understand how frustrating it can be when something as routine as creating a Teams meeting doesn’t display as expected. 

Here are a few places to check that might help you resolve the issue: 
1.Double-check that your default message format is HTML.  

2.Disable and re-enable the Teams Add-in 

Go to File > Options > Add-ins. 

At the bottom, select COM Add-ins > Go. 

Uncheck Microsoft Teams Meeting Add-in for Microsoft Office, click OK, then re-enable it. 
Additionally, some users found that after enabling Microsoft VBA for Outlook Add-in, newly created invitations are appearing normally again. 

3.Check Trust Center settings:   

If you’ve tried the steps above and the issue still persists, consider scheduling the meeting through Outlook on the web instead. This often bypasses local formatting issues. 

I hope this helps. 

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I am an IT admin and have the same issue with 3 of my users. I have had two microsoft support engineers in a meeting and we still have not been able to resolve this, even going down to the registry. I have rebuilt the laptop same result and also signed the user into a new laptop and the issue is present.