What steps should I take when moving email sending from an ESP to my own infrastructure to resolve unexpected Spamhaus listings and deliverability issues with mailbox providers?

Migrating from an ESP to your own infrastructure requires a multi-faceted approach focused on reputation building, authentication, and list management. Experts and marketers emphasize warming up IPs gradually, ensuring proper SPF, DKIM, and DMARC setup, and maintaining clean email lists by importing suppression lists and removing invalid addresses. Monitoring sender/IP reputation via tools like Sender Score and Talos is crucial. Mailbox provider communication is also important, especially in the early stages. Technical factors include having a valid HELO/EHLO domain and understanding that rejection messages from Outlook and Apple often indicate direct IP-based blocks. Avoiding newly registered domains is also advised. Finally, actively monitoring feedback loops, analyzing bounce codes, and understanding that mailbox providers throttle new sending infrastructure is important.

When transitioning email sending from an ESP to your own infrastructure, several key areas need attention to avoid deliverability issues and Spamhaus listings. These include warming up IPs slowly, ensuring proper email authentication (SPF, DKIM, DMARC), maintaining clean email lists (exporting allowlists and suppression lists from the ESP), monitoring sender and IP reputation, and actively engaging with mailbox providers. Analyzing bounce codes, complaint rates (via FBLs) and closely monitoring deliverability metrics are also crucial. Avoid using newly registered domains (less than 30 days old) for email, and understand that mailbox providers may throttle email volume during the initial warm-up phase.

Experts emphasize that when migrating email sending infrastructure, it's crucial to address underlying issues causing blocklistings and rejections. Rejection messages from mailbox providers often indicate direct IP-based blocks, highlighting IP reputation problems beyond general reputation metrics. A Spamhaus DBL listing suggests a problem beyond just a newly registered domain. Resolving DBL listings can improve deliverability across multiple providers. Properly configuring and testing SPF, DKIM, and DMARC is essential. Finally, monitor feedback loops and manage complaints effectively to maintain a good sending reputation.

Technical documentation emphasizes several key aspects of migrating email sending infrastructure to ensure deliverability and avoid Spamhaus listings. Newly registered domains may initially appear on DBLs, but this is typically temporary. It's essential to verify IP and domain reputation using available services, and to configure email authentication (SPF, DKIM, DMARC) correctly. Best practices for bulk sending include avoiding spammy content, making unsubscribing straightforward, monitoring feedback loops, and gradually increasing email volumes. Finally, a valid and resolvable HELO/EHLO domain associated with the sending server is required.