What is the best IP warm-up strategy after an ESP server migration?

Key findings

• Gradual ramp-up: The most critical aspect of IP warm-up is to gradually increase your sending volume over time. Sudden spikes in volume from a new IP can trigger spam filters, harming your sender reputation.
• Prioritize engaged segments: Begin by sending to your most active and engaged subscribers. Their positive interactions (opens, clicks, replies) are vital in building trust with mailbox providers.
• Monitor engagement metrics: Continuously track your open rates, click-through rates, complaint rates, and bounce rates. These metrics provide direct feedback on how your new IP is performing. Learn more about common deliverability issues.
• Consistent content: Maintain consistent email content and sending patterns during the warm-up period. This helps mailbox providers recognize your legitimate sending behavior.
• Timeframe: The warm-up period can vary from a few weeks to several months, depending on the volume and frequency of your sends. A general guideline for new senders suggests distributing volume equally across all mailbox providers (MBPs) over time, as noted by SocketLabs.

Key considerations

• Impact of content sensitivity: If you have time-sensitive content, integrate it with your most engaged audiences initially to ensure high positive interaction. This approach minimizes risk to your new IP's reputation.
• Balancing segments: Mixing highly engaged segments with less engaged ones should be approached cautiously. The key is to avoid triggering spam complaints, which can severely damage your new IP's reputation. Understand why emails go to spam.
• IP re-use: Consider whether your ESP could retain your existing IP address during migration. While often challenging due to infrastructure changes (e.g., data center relocation), it's worth inquiring if it prevents the need for a full warm-up.
• SPF and DKIM: Ensure your SPF and DKIM records are correctly configured for your new IP address. Proper authentication is foundational to good deliverability and is especially critical during a warm-up period. For more information, see Mailjet's advice on ESP migration.

Key opinions

• Prioritize engagement: It's generally agreed that sending to your most engaged subscribers first is the best approach to kickstart a new IP's reputation. This yields high opens and low complaints, which are crucial signals to mailbox providers.
• Audience segmentation is key: Segmenting your audience based on engagement levels allows for a controlled ramp-up, ensuring that early sends generate positive feedback.
• Manage negative feedback: Minimizing spam complaints and unsubscribes is paramount, especially during the initial warm-up phases. Mailbox providers are highly sensitive to these negative signals on new IPs.
• Time-sensitive content: When dealing with time-sensitive emails, prioritize sending them to segments known for strong engagement to mitigate risks on a new IP. This ensures critical messages still reach their intended audience while building reputation.
• Expectation management: Marketers should be prepared for a period of careful management and lower sending volumes initially, understanding that rushing the process can lead to long-term deliverability issues. Bento suggests 30 days for sustainable results.

Key considerations

• Audience expectations: Ensure your audience expects your mail and typically engages positively with it. This context is more important than the exact segmentation strategy on a day-to-day basis.
• Managing mixed segments: Sending to a less engaged segment after a highly engaged one might not be problematic if the content is still relevant and unlikely to generate spam complaints.
• Communication with ESP: Understand your ESP's migration plans fully. While keeping an existing IP is often ideal, sometimes a new IP is unavoidable due to infrastructure changes. For more on this, see how email reputation transfers during IP warming.
• Leveraging existing engagement: If daily sends target different segments, leverage any highly engaged segments by holding some back for subsequent sends to ensure consistent positive interaction across the warm-up period.

Key opinions

• Inescapable warm-up: Even with infrastructure changes that force new IPs, warm-up is required. Proper planning can mitigate significant deliverability issues.
• Positive engagement focus: The core of successful warm-up is maintaining high positive engagement (opens, clicks, conversions) and low negative reactions (spam complaints, unsubscribes, bounces). Starting slowly with highly engaged recipients is crucial. For more on this, check best practices for dedicated IP warm-up.
• Reasons for new IPs: ESPs may have valid technical reasons (e.g., migrating to deprecated or new platforms, or entirely different server architectures) that necessitate moving customers to new IPs, making it difficult to retain old ones.
• Planning is paramount: Extensive planning and communication with the ESP are vital. While pushback to retain IPs is advisable, prepare for the possibility that new IPs are unavoidable and a warm-up plan must be executed carefully.

Key considerations

• Infrastructure limitations: Understand that an ESP relocating to a different data center or renumbering IPs from a new provider often makes retaining old IPs technically unfeasible, despite a client's preference.
• Proactive notification: Forced IP changes should ideally come with significant prior notice and client agreement. If not, it strengthens the case for negotiation or demanding more support during the warm-up.
• Risk management: While painful, a well-executed warm-up minimizes deliverability issues. This includes starting with the most engaged audience and focusing on metrics that demonstrate positive sender behavior. For troubleshooting, consider resolving IP blocks and deliverability issues.
• Consistent send patterns: Maintaining consistent send volume and frequency during the warm-up, even if starting low, is key to building a predictable and trusted sender profile with mailbox providers.

Key findings

• Volume scaling: Documentation typically provides daily volume increments and maximum send limits for the warm-up period, often recommending starting with very low volumes (e.g., a few thousand emails) and gradually increasing. Twilio SendGrid outlines their IP warm-up guidelines.
• Engagement first: Always prioritize sending to your most engaged subscribers who are likely to open and click. This generates positive signals that mailbox providers use to evaluate your IP's trustworthiness.
• Authentication setup: Proper configuration of SPF, DKIM, and DMARC is fundamental. These authentication protocols confirm your legitimacy as a sender and are crucial for reputation building on a new IP. Ensure your DMARC, SPF, and DKIM are correctly configured.
• Monitor and adapt: Utilize postmaster tools (e.g., Google Postmaster Tools, Outlook SNDS) and your ESP's analytics to monitor deliverability, bounce rates, and complaint rates. Adjust your sending volume and strategy based on these metrics.

Key considerations

• Patience is essential: Rushing the warm-up process can lead to immediate filtering and long-term reputation damage. Adhere to recommended schedules, even if it feels slow. Email Vendor Selection provides guidance on establishing a positive reputation.
• DNS setup: Ensure all relevant DNS records (A, MX, SPF, DKIM, DMARC) are properly configured and propagated for your new sending infrastructure.
• List hygiene: Clean your email list before starting the warm-up to remove inactive or invalid addresses. Sending to a pristine list minimizes bounces and spam trap hits, which are detrimental to a new IP.
• Domain warming: While IP warm-up is specific to the IP, simultaneously warming your sending domain (if new or significantly changed) is also essential for holistic sender reputation. This often involves similar gradual sending practices.