By what mechanism is mail exchanged in the Third Imperium? I know that Xboats and the XBoat routes have the responsibility of carrying mail, and as of T5 that is in the form of an Xboat mail wafer, but what actually happens? If I'm a lowly resident of Harappa (Solomoni Rim) and want to send a letter / message to someone on Feneteman in the Spaniard Marches what exactly do I do? Make the pilgrimage to the starport, borrow a terminal with which to encode to a wafer to be loaded on a ship that will jump one step closer to Feneteman, and the messages from that ship then get sorted based on their destination and loaded onto the appropriate wafer of something headed in the right direction? 

How do you envision the actual mail process to work? Is interstellar mail delivery reliability high? Can you ask for a delivery receipt (perhaps delivered to you 80 or 100 weeks later)? How expensive is it to send inter-system mail?