I'm not sure if you guys have dealt with ISP blacklists before, but I think there is a good chance hint.io will never be able to reliably reach an inbox again.

I'm not sure if you guys have dealt with ISP blacklists before, but I think there is a good chance hint.io will never be able to reliably reach an inbox again. Sending emails to white-listed addresses is hard enough to get right, let alone sending to 1.5 million arbitrary email addresses.