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?

Key findings

• Unexpected listings: Newly registered technical domains (e.g., HELO domains) can be listed on blocklists like Spamhaus DBL even before sending any email, suggesting that domain age is a factor in reputation.
• IP-based rejections: Mailbox providers such as Outlook and Apple may reject emails from new IP addresses due to internal blocklists, even if those IPs do not appear on public blocklists. These rejections can be influenced by IP subnet or autonomous system (AS) reputation of the hosting datacenter.
• Domain vs. IP reputation: Some mailbox providers apply DBL listings (which typically target 'from' domains) to the HELO (envelope) domain as well, impacting delivery regardless of the sending IP's status.
• Warm-up challenges: Building reputation for new IP addresses and subdomains from scratch is a slow process, often requiring months to gain acceptance from various mailbox providers.
• Root cause: While infrastructure issues might seem apparent, underlying problems in user acquisition processes, consent management, and email content are often the true drivers of reputation decline.

Key considerations

• Domain age: Avoid using domains younger than 30 days for production email sending to mitigate initial reputational hurdles.
• Direct engagement: When facing rejections, directly contact the postmaster teams of the affected mailbox providers. They can offer guidance and sometimes grant temporary volume access to help warm up new IPs.
• Reputation portability: Leverage existing good domain reputation to bootstrap new IP reputation, and vice-versa, especially if switching to a new subdomain or IP range. Consult expert insights on email deliverability issues.
• Comprehensive checks: Beyond public blocklists, consider that mailbox providers use a wide array of internal factors, including AS, registrar, CIDR, hosting company, and DNS provider reputation, as well as the history of previous IP owners.

Key opinions

• Unexpected DBL listings: Many marketers are surprised when their new technical domains (e.g., HELO domains) are listed on Spamhaus DBL even before sending any email traffic.
• Helo domain impact: Mailbox providers like Apple and Yahoo may apply DBL listings to the HELO (envelope) domain, not just the 'from' address domain, leading to unexpected rejections.
• Datacenter reputation: There can be significant differences in deliverability between datacenters, with some experiencing immediate rejections from major mailbox providers, even for IPs not on public blacklists.
• Frustration with traditional MBPs: Some express frustration with mailbox providers like Hotmail, Yahoo, and Apple, perceiving their filtering rules as less sophisticated or transparent compared to Gmail.
• Increased complexity: Setting up and maintaining a self-hosted email sending infrastructure is considered much trickier now than in previous years.

Key considerations

• Patience during warm-up: Be prepared for a multi-month period to establish new IP and domain reputation with mailbox providers, especially those with more stringent filtering.
• Proactive communication: Actively engage with mailbox providers' postmaster teams when encountering blocks or rejections to understand the specific causes and work towards resolution. For detailed steps, consider proven email blocklist removal methods.
• Subdomain strategy: While using new subdomains avoids DNS complexity with old ESPs, it means starting with fresh domain reputation. Re-using existing, well-reputed subdomains, if possible, can significantly aid the transition.
• Understanding reputation indicators: Recognize that mailbox providers use various reputation indicators beyond just IP and domain, including autonomous system (AS), registrar, CIDR blocks, hosting company, and DNS provider history. Improving your overall sender reputation is critical.

Key opinions

• Holistic reputation: Email reputation extends beyond IPs and domains to include AS, registrar, CIDR, hosting company, DNS provider, and even DKIM keys. Each mailbox provider uses its own unique formula.
• List hygiene first: Problems with user acquisition, consent, and content are usually the root causes of reputation issues, rather than infrastructure alone.
• New infrastructure skepticism: Servers and domains that have never sent email before appear suspicious. Starting everything new simultaneously requires a slow, deliberate reputation build-up.
• IP-based blocks: Rejections with messages like 'IP address on the blocklist' from multiple major MBPs often indicate explicit IP-based blocks, suggesting issues within the network neighborhood or from previous IP users.
• Spamhaus DBL reasoning: Spamhaus does not list newly registered domains on its DBL without other contributing factors. Domain age is a factor, not the sole reason for a listing.

Key considerations

• Contact postmasters: Contacting mailbox provider postmaster teams is crucial for resolving rejections and gaining volume access for new IPs. Yahoo and Microsoft (Outlook) provide postmaster sites or specific contact forms. Diagnosing issues directly is key.
• Domain re-use benefits: If possible, using the same, well-reputed sending domains from your ESP on your new infrastructure can help bootstrap IP reputation, as domain reputation can transfer.
• Transparency is vital: When seeking help, provide specific details like IPs and hostnames. Without this information, it is impossible to accurately troubleshoot deliverability problems.
• Understand internal blocklists: Public blocklists do not always correlate with the internal data used by mailbox providers. A clean result on a public list does not guarantee acceptance from an ISP. Learn more about how email blacklists actually work. Consider the best practices for new domains from Spamhaus.

Key findings

• Spamhaus domain age policy: Spamhaus considers domain age as a factor in its reputation assessment for newly registered domains but does not automatically list them on the DBL solely due to recent registration without other indicators of suspicious activity.
• Direct communication channels: Mailbox providers like Apple, Microsoft, and Yahoo provide specific postmaster pages and contact forms for senders to address deliverability issues, including IP blocklistings and rejections.
• Internal blocklists: Bounce messages from mailbox providers often indicate blocks originating from their internal systems, which are not always reflected on public blacklists.
• Proofpoint escalation: For blocks from services like Apple (which may use Proofpoint), there is often a specific link or process provided in the bounce message to escalate the blocked IP directly to Proofpoint for review.

Key considerations

• Review postmaster sites: Regularly consult the postmaster pages of major mailbox providers (e.g., Apple iCloud Mail, Yahoo Senders) for their specific guidelines on bulk sending, authentication, and troubleshooting deliverability issues.
• Utilize sender support forms: For Microsoft (Outlook/Hotmail) issues, use their dedicated support request form for unblocking rather than general contact methods.
• Understand bounce codes: Analyze bounce messages carefully, as they often contain specific error codes and links that direct you to the exact reason for rejection or the appropriate delisting tool.