Play-By-Mail is a throwback to the 70s, 80s and 90s when there was an active gaming genre called PBM games.
A play-by-mail game (also known as a PBM game, PBEM game, or a turn-based game) is a game played through the postal system, email or other digital media. Correspondence chess and Go were among the first PBM games. Diplomacy has been played by mail since 1963, introducing a multi-player aspect to PBM games.
How do PBM games work? In the past, players would play PBM games by sending their ‘moves’ or ‘orders’ (called a Turnsheet) via the postal system to the game moderator (who processes the orders) who then sends the results back to each player…thus the term Play By Mail Games!
Today, while PBM games still exist, there are just a handful still running compared to hundreds of active games back in the hobby’s heyday. This is largely due to the rise of the Internet.
Nowadays most PBM games make use of the Internet and/or email to communicate with players.
A PBM game can be as simple as a human running an ordinary Dungeons & Dragons game, or a computer moderating a fantasy strategic/role-playing game with a complex set of rules and many hundreds if not thousands of players.
Why play PBM games? Well, even though the commercial games are expensive, they offer some things that some people have a hard time finding face to face — good opponents, convenient playing times, and games with lots of hidden information, team building and diplomacy (both inside and out of the game). Non-commercial games can offer the same benefit, as long as the people running it are dedicated.