One of my first professional philatelic tasks, some forty years ago, was to assemble old correspondences for sale. You saw these more in those days than you do today, but what they were were large selections of letters that had been sent between correspondents over a period of years. Usually these were things like weekly letters between brothers and sister or parents and children who fate and circumstances had parted. Remember, in 1860, if your daughter and her husband moved from Ohio to California, the high probability was that you would never see her again. Her letters became a very real record of what was left of the relationship. They were saved and cherished and reread. And often these correspondences were kept in families long after the correspondents had passed away. Philatelists and postal historians collected them because they usually had the envelopes with stamps and postal markings. Such correspondences represented the intersection of philately and the real world and were actively sought out by the last generation's philatelists.
There is a very distinct tone and feel to most people's writing. We are well aware of how someone "feels" to us in conversation. But that same tone pervades their writing, and when one reads through a large correspondence from a brother to a sister written over twenty years, you get a good sense of the personality of the people involved. One of the early series of letters that I put in order was between two brothers, both ministers who were separated by over a thousand miles and who would never again meet in person. We had only one brother's letters as they had been saved by the other brother. Over the course of the correspondence, you watched the man's children grow, his relationship with his wife mature, and in the last few letters the pain and anguish of finding his young daughter "with child out of wedlock." Researching the local papers, we found out that the minister died a few weeks later. I couldn't sell that correspondence, and we donated it to the county historical society from where the letters originated.
So those of us who grew up reading the writing of individuals who were not professional authors lamented the fact that so many people stopped writing letters in the telephone age. It seemed like the art of personal correspondence was dying. Email has changed that. People today write many thousands of words with the average user of email writing nearly The Great Gatsby's worth of words per years. Much of it is business and cursory communication, but many people have returned to the art of letter writing to keep in touch with friends and relatives.