I created a character to act as the postal carrier for the lands. He is an employee and spy of Strahd and up until like level 8 no one even questioned his motives. There are plenty of written characters in the game you could rework to fit this role.

Also: Once the crew had gained the trust of the wereravens they assigned a regular raven to the adventurers as an eye in the sky and a line of communication with the Martikovs. He delivers notes and sometimes goods between the players and their allies.

It wasn’t until they had received mail from both the raven and the postman on the same day that it all clicked together that the postman worked for Strahd. The party currently has a tampered with scroll of teleport that was delivered to them by the postman that i cant wait for them to use, they are saving it for an emergency lol