1. A mandatory ticky box on the challenge creation page. "I understand that I may have access to challenge participants' email addresses and that use of those email addresses for any purpose other than running the challenge will lead to the termination of my account."
2. A notice on the challenge signup page along with the other notices in the blue box: "Challenge maintainers may have access to the email address associated with your AO3 signup for purposes of communicating with you about the challenge."