Typically users don't want to give you email unless you prove them it's worth it. So instead of making email mandatory for registration, you can now try showing

Typically users don't want to give you email unless you prove them it's worth it. So instead of making email mandatory for registration, you can now try showing articles around improving there game skills or ask them if they want reminders. Let them opt in on emails. This is called permission marketing. Seth godin has a while book around it.