Back when I ran a mail server for a small business, I would see the spammers literally going through all the permutations of email addresses for a domain. In th

Back when I ran a mail server for a small business, I would see the spammers literally going through all the permutations of email addresses for a domain. In the logs you'd see: failure to send to a@example.com failure to send to b@example.com ... failure to send to aa@example.com etc.