Does playing correspondence chess improve your game? My rating is around 1200 and I want to improve my chess.  Will playing correspondence chess improve my game?
Whether or not playing correspondence chess will help you to improve depends a lot on how you play.  If you move after a quick look at the position and use it more like a Blitz game with the possibility of pausing, then I do not think you will improve much.  If on the other hand, you use it to study the relevant openings, pawn structures, endgames, etc. then they can provide a real asset for improvement.  In particular if you combine them with some theoretical inputs from books etc. as you can then immediately try to turn the things you learn into praxis (which means you really learn them).

Another thing that may be worthwhile is to keep notes during the games of what moves you were considering and how you evaluated them.  In the post mortem you can then check your analysis and evaluation of the game and spot areas for further study and improvement (e.g., good moves you did not consider, or moves where your evaluation deviates strongly from that of, say, a chess engine or a coach).

Of course not everything improves by correspondence chess.  For example, if in OTB games you often hang your pieces or fall for simple tactics, then you really need to work on this separately.  The fact that you can try the moves in correspondence chess should help to eliminate these simple mistakes from your correspondence games but they will likely be back in OTB games.