Message Header Analyzer mail app.
This is the source for the Message Header Analyzer. Install the app from the store here: https://store.office.com/message-header-analyzer-WA104005406.aspx
Because MHA requires the ReadWriteMailbox permission it can only be installed by the Administrator through the Exchange admin center. Here are some steps I put together:
- In Office365, go to the Exchange Admin Center.
- Click on the Organization tab
- From there, select the add-ins tab
- Click the Plus icon/Add from the Office Store
- A new page will load for the store
- Search for "Message Header Analyzer"
- Choose MHA in the results
- Click Add
- Confirm by clicking Yes
- Back in the Exchange Admin Center, refresh the list of add-ins
- You can now edit who the add-in is available for
A Note on Permissions
In order to get the transport message headers I have to use the EWS makeEwsRequestAsync method, which requires the ReadWriteMailbox permission level. See the article Understanding Outlook add-in permissions for more on this. If I could request fewer permissions I would, since I only ever read the one property, but I have no choice in the matter.
When REST is more widely available, and a few REST specific bugs are fixed, I'll be able to switch to REST and request a lower permission level.
Here is a standalone Message Header Analyzer running the same backend code as the MHA app: https://mha.azurewebsites.net/pages/mha.html