In version 1.x on any difficulty level, and in version 3.x on levels below Hero, Raillag needs only Chaos.
As a Warrior, I caught up with all the messengers even without Logistics. In fact, I didn't even need to catch up with anyone. I ended my turn one step away from the castle. On the next turn, I captured the castle and ran to take a position at the large crossroads. The messengers came to me themselves. The same thing happened with the hero. Only the second or third messenger hit Raillag so hard that I preferred to reload and not engage them.