At the end of the Civil War, the Dead Letter Office had 4.5 million undelivered letters. Thousands of people swept away from their families in war time tried to connect through the mail, but many had extremely limited literacy and virtually no knowledge of the postal service. This Photo Sleuth article on Slate goes into the details of how the Dead Letter Office tracked down the recipients of many of those lonely letters. They even talked to one of our own, long-time L.W.A. member Ashley Bowen-Murphy, about the fate of letters which could never be identified and delivered.
One thing the Dead Letter Office did was establish a museum for some of the more particular or poignant artifacts they had been unable to forward.Among those items were thousands of cartes de visite, photographic portrait postcards, of Civil War soldiers. The museum displayed them at various times over the years and even send the cards on exhibit to other cities in hopes they would be identified and claimed. A purported 2,000 of cards were identified in this fashion. However, as time went by, fewer and fewer had any hope of finding their recipients. When the DLO closed in 1911, the cards were sold into private collections. One ended up with the author of the article and prompted this research. I encourage you to all read the full article and Ashley's article from the citation. It's fascinating stuff.