While dozens of blocklists have faded into history or irrelevance over the past 25+ years, Spamhaus remains the heavyweight when it comes to IP and domain reputation. They run one of the oldest anti-spam blocklists in existence, still trusted by major mailbox providers and internet service providers (ISPs) worldwide. If your sending IP or domain lands on a Spamhaus list, you are going to have deliverability problems. And following in the footsteps of Google, Yahoo, and Microsoft, Spamhaus has officially published its own comprehensive Spamhaus Sender Guidelines to spell out exactly what it takes to be a good sender and...