Choose the right channel before you send.
For a non-sensitive lead, explain what the material shows, where it came from, and whether there is a deadline. Ordinary email is not anonymous or end-to-end encrypted.
Confidential or sensitive material
Do not attach it or describe it in ordinary email. Request a safer channel using only a safe reply method and a general deadline. The Human Input will agree on the channel before receiving material; this request itself is not anonymous.