[Rami114]

Or, you're going to use something rock solid to encrypt your message and use some sensible approach to obscure your signals.

Not an expert here, but if you don't want to give out signals by the mere fact that you're sending an email with encrypted content, set something up to send encrypted messages regularly, at scheduled intervals, and allow a real message drop in on the queue. As long as your encryption method reveals nothing about the cleartext you can put something in the cleartext to notify your recipient this one is real. I say this in the hope nobody who needs these things for life and death situations will look at HN for advice.