This message is tucked away in Gotham's Public Library system (specifically in city maps and blueprints). Any traces on it resolve to public wireless hubs.
From: Oracle [124.2.142.532.4334@0121.332.32.00.4.2] To: Batman Subject:Recent Events
We need to talk about what happened. I have a lot to tell you. You can come see me. I'm home, if you didn't already know that.