I think the idea is that you can generate the MD5 hash of all, say 8 letter, @gmail.com addresses trivially and since the email hashes used for targeting don’t

I think the idea is that you can generate the MD5 hash of all, say 8 letter, @gmail.com addresses trivially and since the email hashes used for targeting don’t have a salt, it’s a one time “expense” to build the reverse lookup table