Messengers
We've had some questions about messengers and letters recently-- and the rules about them have always been vague. For that reason, I've created a set of guidelines for you all to refer to as regards messengers. They follow here:
Assume messengers exist as NPCs. They would be mostly birds (humans, of course, in Archenland).
In Sted Cair and Andale, you may assume that you can usually find a messenger (or at least a merchant going in the right direction) within 2 days of composing the message. (In the castle, you can assume immediacy.)
In Lantern Waste, Barfield/Beruna, and Lancelyn Green, you can assume you could find one within 4 days.
Everywhere else, assume you could find one within the week. (In Ubel, good luck, unless you're Maeta).
Add the number of days it takes to travel to the region your message is intended to go to. In winter, consider adding another day or two to this (please do add at LEAST a day or two if the messenger has to cross the pass between A-land and Narnia in winter). Keep in mind that birds can generally cross two regions in one day.
Again, I will restate that this is a set of guidelines. You are free to work within the boundaries of reason when it will make for a better story. A message could easily be delayed months if carried by a bad messenger or if something happened to the messenger. It could be that there is a messenger in your area while you are still writing the message, and so the message only takes as long as it takes to travel to reach the recipient. Please consider, however, that in most cases, this means a longer period of time. Circumstances which shorten the length of time will be very rare.