A black hat sender is a sender or company who sends email to recipients that didn't specifically requested to get emails from that sender. It is somebody that delivers unsolicited emails to recipients that never requested them.
Not all black hat activity is intentional, though. Even senders who have their recipient's permission but send an excessive amount of email or who send at an alarming frequency may be flagged by users as “spam”. These senders will be identified by the recipients’ ISP, which may throttle the sender's email, send it to spam traps, or totally block the emails.
If your emails are not getting the clicks and opens you expect, you may want to re-evaluate your sending habits. Also, please take a look at our email deliverability tips for help in being a white hat sender.
For more information: