k-Anonymity. In other words, "I have hashed my e-mail address, here's the beginning part of the hash: 0deadbeef0, tell me if you have anything matching that." "Yup, I have something that hashes to 0deadbeef0123456789abcd, associated with these breaches, and something else that hashes to 0deadbeef0abc1056886516, associated with those breaches." Plaintext is not exposed, and you're not even exposing the whole hash, so GL to anyone trying to find out which if the hashes (if any) is yours, let alone what the plaintext was.

https://blog.mozilla.org/security/2018/06/25/scanning-breach...