How to link an iCal event to an arbitrary message in Mail app.

Sometimes I want an iCal event to link to an e-mail message in Mac OS X’s Mail application, but not infrequently the message text does not contain a date for easily creating an iCal event. (You know, when the dashed box appears around a date hovered by the mouse cursor...)

So here is what I do to add a link to such a message, anyway:

1. First, display the message in Mail.app
2. Choose the Long Headers command from the View/Message submenu
3. Search for the Message-Id header, then select and copy its value
4. Create or edit the desired iCal event
5. In the url field enter message: followed by the copied Message-Id value
6. Benefit!

As an example, this is what the Message Id header looks like in Mail.app:

And this is the text that would be entered in the iCal event’s url field: message:<B00B1E51.9711018@p3k.org>