I hope you are not intending to override the user’s email notifications settings in their preferences! As my daily routine includes working through all the Discourse communities I am a member of I do not want any emails from any of those communities. I pick up the award of badges when I next participate, which is at least once a day but typically more often (for example this message was written during my second of the day here at Meta Discourse). Even if I did not visit regularly I would object to getting emails that I had explicitly opted out of receiving.