challenge
If you resign before the first four moves have been completed, there isn't a change in rating. That said, if it is an issue for you, only challenge people that have a really fast average time to move.
I'm on my mobile during the day and if someone sent me a challenge and I decided to play, I might accept it and may make a move if I'm white. That completely depends on how much time I might have.
Then, since it's correspondence, maybe they want to look through your games and try to figure out what you play and prepare some surprises for you ![]()