This was traditionally played by players exchanging moves via letters sent by post.

Naturally people use the internet more these days, but with a lot of time allowed between moves to keep the slow pace of correspondence chess.

Allowing this amount of time between moves completely changes the character of the game. There’s ample time of deep analysis and research. There’s more incentive to leave the beaten track if you need to push for a win.

It’s an extremely different game to over-the-board chess.