[Ui1ahcex]

Additionally to what others mentioned, Dnd Beyond [1] has a quite active play by post board on their forum. It's great to get started, but games tend to rarely go to the end of the campaign and stop after a few months. It's still a good thing as a first experience.

After that, I would recommend to find friends to play by mail. Somehow, I noticed players less easily give up the game when they're friends. Simply by talking regularly about your first games is usually enough to get other friends interested. Just don't push it on them and let them come by themselves, as it's quite a commitment and will be felt as a burden if they feel they're playing with you just to be nice to you.

[1] https://www.dndbeyond.com/