Overview: the Microsoft Message Header Analyzer tool can be useful to diagnose problems with email. The tool can be found at https://mha.azurewebsites.net/ Here's a quick example of how to use it in conjunction with Outlook.
In this example we want to troubleshoot an email that we tried to send using Outlook and an Office 365 account.
Double-click the email in the Sent Items folder (or wherever your email is):
Now click Properties, select all the text within the "Internet headers" field, right-click and choose Copy:
Navigate to https://mha.azurewebsites.net/ in your browser, paste in the internet headers, and click analyze:
If you'd like us to also analyse the headers for you then please save the copied text as a plain text file (Windows Notepad will do) and attach the file to a ticket; please do not paste the text directly into a ticket as our ticket system does not preserve all of the information in it's raw form unless you attach a plain text file.
Further tools: other similar tools that may help in troubleshooting Office 365 and Outlook can be found at https://testconnectivity.microsoft.com/