This is the same as what happens when you use PGP. You have a timestamped message and a clear link between sender and recipient. If you need to hide the fact that you are communicating with a person in particular, Syme (or PGP for that matter) may not be the right tools.
You've set your sights much too low, and it's unfortunately going to limit your product's market value.
Hiding metadata is a difficult problem to solve, but it's vital.