Messengers used to be very important in the ancient world as they were the only way to pass information to others over a long distance. As time passed, people started using other ways to transfer information, at first, it was pigeons, and for a long time that continued. As time passed, people set up post service to send communication over a long distance. Postmen were very important during all of the 19th and 20th centuries and especially during the first and second world wars.
And as the internet was used more and as mobile communications improved people were able to connect to each other instantly, post office and postal officials were used less to transfer letters but rather to ship items now and people were less and less dependent on postmen for transferring their letters as they could communicate with each other.
And then after couple hundred years, even that task was handled by drones and robots. People were now not dependent on other people for receiving their packages and letters on other people. Communication was instant for many years now and now the packages were received instantly or rather way quicker than in the past. Now the postmen were no longer required and the post office was now handled by the robots. The world was fully automated humans are totally dependant on machines and most of the tasks were now handled by robots.
It was theorized for a long time that solar flares can be very harmful to the earth but so far we got lucky but no more as in quick successions and without any warnings, solar flares reached closer and closer to the earth and fried up all the equipment set up on the moon, then even bigger flare rose up to destroy all the various satellites in the earth's atmosphere. And just like that, all the services came to a halt no phones, no Internet, no GPS. This caused more and more issues and without the internet, the public utilities failed that were being handled by robots and over the Internet. Electricity went out all over in some time. The world went dark almost in a blink. Now it was like people were back in the dark ages but they had no experience of how to survive on their own.
All the countries experienced rapid deaths as people panicked and rioted and before things can be brought under control. Almost 2 Billion people were lost around the world during this time. Even more, people were lost as there was suddenly a scarcity of food and other resources. But soon enough people realized that they would have to come and work together to survive. The entire society was back to a standstill with no travels and communications over a long distance.
With time people started working together and to build their infrastructure as per 18th-19th century standards. They also worked to set up the postal network again and thus the importance of Postmen was restored.