I've had another crack at this and got very close..
This works and brings up a new email window with the user's email address in the correct bit, however i can't get the Id placeholder to work.
my question is, can placeholders work in this way? I've tried {_Id} and {Id} and neither bring the incident number through.
Any ideas?
by using:
Application: explorer.exe
Prefix: "mailto:
Postfix: ?Subject=Ticket Reference: {_Id}"