What is a black hat sender?

Black hat senders are email senders with a poor sending reputation. They are often blacklisted and their emails are sent directly to spam folders by ISPs. Black hat senders are usually businesses that send unsolicited, unwanted emails in bulk or too frequently. This behaviour is considered suspicious by ISPs, who then block or send the emails to spam folders. Black hat senders have poor deliverability and their emails are rarely seen by the intended recipients. To avoid being flagged as a black hat sender, it is best to follow deliverability guidelines.