Yes, they offered to buy the emails, not the addresses, the content. They said it was to train some AI programme and that these e-mails had to be in English (at least C1 level) and have at least one reply.
Yes, I mean the actual email, not just addresses. I am a freelancer who works via Upwork. A client I had a contract with for a different job (voice recording), made me this offer 0.40 USD per email. The offer came via a private message.