Spamhaus is a well-respected organization that monitors IPs and domains for sending spam, providing data to ISPs and law enforcement. They use spam traps to catch senders who don't practice good list hygiene, which are email addresses used solely to catch spammers. Spamhaus takes a strict stance on handling bounces and spam complaints, disabling emails after one hard bounce unless manually intervened. To keep lists clean, it's essential to avoid sending to spam traps and measure engagement in marketing emails, as transactional emails have limited options for tracking engagement. The organization highlights the importance of separating marketing and transactional email, reacting differently to spam traps hit by each type, and encourages Postmark users to use their API and web hooks to fix issues and ensure successful delivery of transactional emails.