Caledon Royal Mail
The Principality of Caledon's equivalent to the Imperial X-boat system. This system serves the Principality, the Grand Duchy of Douglass and a few systems beyond the Principality.
Non-Canon
The Caledon Royal Mail (CRM) has a similar mission to the Imperial X-boat system - but with some significant differences.
Courier Service
As the Principality is much smaller than the Imperium, and most of the key stops are 1-2 parsecs apart, the RCM's courier boats tend to work the same route repeatedly until overhauled. Higher-traffic routes will have more boats assigned, and those boats will largely bounce back and forth between the same systems until overhauled - when they may be reassigned. For example, there are five Courier boats assigned to the Caledon-Cuillen run; four in service (providing twice-a-week service between the systems), and one on standby.