Sending, receiving, and organizing email in Outlook.com
Copied from Mohammad, he has laid things out better than I have.
"The message Id should be this expression because they are using a single quote (') after "@" which is causing the flow failed and return error "Id is malformed." It should be
In the dynamic content popup, click on "Expression" tab.
Paste this:
triggerOutputs()?['body/Id']
Click OK (or Update).
Now mine is working 100%"