I was inside Alftand reading a journal and messing with stuff, and turned to look left. An imperial was there, and he went running off! He wasnt running from me, i could talk with him fine. But...how did he get into that location? You have to go out of your way to get there, so...

Its weird right?

An imperial courier passed through the ragged flagon, into the cistern, and out of riften.
A Stormcloak courier appeared when i was in blackreach.
An imperial courier appeared in sovergarde

Sometimes it is nice to see weird things happening, dont worry i got these encounters too.

I kill couriers.....no witnesses. Sometimes they have cool letters not addressed to my character.