In the wake of each innovation new threats are catching up with us. The history of mail is one of speeding up and finding ways to prevent unwanted interferences.
About horses and ponies
Couriers in ancient Persia rode rapidly from station to station, changing horses at each station. The Mongols did this, too, and much later in the United States the Pony Express used a similar system to deliver mail across the American continent.
It took a long time for messages to reach their destination. And there was the challenge of protecting the stations from robbers.