Adding a Disclaimer to Calendar Meeting Requests

Remind Meeting Attendees of Protocol and Expectations

Adding a disclaimer (aka auto-signature) to Exchange Online messages is a well-trodden path. The process is straightforward: create a transport (mail flow) rule to add some disclaimer text and enable the rule. You can include HTML-formatted text and insert attributes about the sender into the disclaimer text such as their name, title, and telephone number. The Exchange transport service will apply the text to every outbound record. This process works even with protected (encrypted) messages because the Exchange transport service is able to decrypt and re-encrypt messages. Just about the only complication is to include an exception condition in the rule to avoid applying the same disclaimer to the replies for an original message as that creates disclaimer upon disclaimer, which isn’t good.

All good, but what happens if you want to insert a special disclaimer into the messages sent for calendar meeting requests to remind internal users about meeting protocol, privacy, or etiquette (like “please tidy up the meeting room when you are finished”).

Look for X-Headers

The solution is to use a transport rule that checks for the presence of an X-header added by Exchange to calendar meeting requests. Some quick browsing of the headers of a meeting request using the Outlook Message Header Analyzer add-in revealed the presence of a header called X-MS-Exchange-Calendar-Originator-id, which seemed like a good bet (Figure 1).

Analyzing message headers to find calendar indicators
Figure 1: Analyzing message headers to find calendar indicators

It didn’t take long to create a rule (Figure 2) to check if this header had a value (I used part of the distinguished name of the meeting originator) and apply a disclaimer. I also added an exception to make sure that the disclaimer wouldn’t be applied if the text already existed in the message.

Mail Flow rule to add disclaimer to meeting requests
Figure 2: Mail Flow rule to add disclaimer to meeting requests

X-MS-TrafficTypeDignostic might be an even better header to use. This header contains the name of the originating server and “MeetingMessage”, so you could check for that value.

The Disclaimer Works

Adding a rule is one thing. Seeing it work is another. Fortunately, the rule worked (Figure 3) and the disclaimer shows up in meeting requests.

Disclaimer text in a meeting request
Figure 3: Disclaimer text in a meeting request

I haven’t done much testing to verify that the disclaimer works in all circumstances. In some circumstances, adding a disclaimer to a meeting request can cause a receiving system to process calendar requests as if they were normal email, which means that the recipient loses the ability to respond to the request. In this case, the rule only applies to messages sent internally, which was the original request. After a day or so of the rule being in place, it seems to work reasonably well and certainly is a basis for further development if this is needed by an organization.

It’s amazing what you can do with a little knowledge of how Exchange works…


Chapter 17 of the Office 365 for IT Pros eBook explains mail flow rules in great detail. It’s worth reading!

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