frezik

“Hashed emails”. Besides the fact that they can match up a hash from one source to a hash from another source to link them to the same person, emails often have enough predictability to break the hash. Assuming they all end in “@gmail.com”, “@outlook.com”, or “@yahoo.com” will get you the vast majority of emails out there. Unlike a good password scheme, people don’t shove a lot of random data into their email addresses.