What is the best IP warmup strategy for email sending?

Key findings

• Volume sensitivity: IP warmup is essential for significant daily send volumes, such as ramping up to millions of emails per day. For very small volumes (e.g., under a few hundred daily emails), a dedicated warmup might not be strictly necessary.
• Gradual increase: The core principle involves starting with low email volumes and systematically increasing them over time, giving ISPs a chance to assess your sending behavior.
• Engaged audience focus: Initial sends should target your most engaged subscribers. Their positive interactions (opens, clicks) send strong positive signals to ISPs, building a solid reputation.
• Consistent sending: Maintaining consistent sending patterns and volumes during the warmup period is key. Sudden spikes or drops can negatively impact your reputation.

Key considerations

• List segmentation: Segmenting your email list to identify and target your most active users for the initial warmup phases is highly recommended. You can learn more about best practices for dedicated IP warmup.
• Avoiding fatigue: If your brand already sends daily emails, re-sending to the same engaged subscribers during warmup might not cause fatigue or spam complaints. However, if this introduces a new or different pattern, consider rotating your engaged audience.
• Clean list hygiene: Always start with a clean and validated mailing list to avoid bounces and spam traps, which can harm your nascent reputation. This is a critical step for building a strong email reputation.
• Monitoring metrics: Closely monitor deliverability metrics such as open rates, click-through rates, bounce rates, and spam complaint rates. Adjust your strategy if you see negative trends, as this is part of understanding your email domain reputation.

Key opinions

• Engagement-driven volume: It is crucial to grow sending volume in conjunction with good engagement. The success of the warmup relies heavily on positive recipient interactions.
• Context is key: Small initial send volumes (e.g., 50-125 subscribers) are often too small to require a formal IP warmup unless the typical daily volume is similarly low.
• Flexibility in strategy: Both methods of gradually increasing volume (sending to the same engaged users or new engaged users) can be effective, depending on the specific circumstances of the sending pattern.
• Avoidance of fatigue: The primary concern with repeatedly sending to the same engaged list during warmup is potential recipient fatigue, which could lead to increased spam complaints if the sending pattern deviates from normal.

Key considerations

• Existing send patterns: If recipients already receive near-daily emails, increasing volume by adding more engaged subscribers to the existing set (rather than rotating) is often suitable, as it aligns with their expectations.
• List segmentation for engagement: Marketers frequently segment their email lists to identify the most engaged subscribers, making them ideal candidates for the initial stages of warming up an IP address.
• Cleanliness of lists: A clean email list is paramount. Marketers often advise using a validation tool to remove non-real or risky addresses before starting the warmup process to prevent your email address ending up on a blacklist.
• Patience and consistency: Many marketers reiterate that IP warming is a methodical process requiring consistent sending over several weeks or months, not a quick fix. This careful approach helps avoid email deliverability issues.

Key opinions

• Volume relevance: Warm-up is critical for high-volume senders, typically those sending hundreds of thousands to millions of emails daily. For very low volumes, dedicated warming might be overkill.
• Engagement is paramount: The success of any warmup strategy hinges on the positive engagement signals received from recipients. Opens and clicks are far more important than just send volume.
• No one-size-fits-all: While specific warming schedules exist, the underlying principle of gradual volume increase coupled with strong engagement is more important than the exact method of list rotation or repetition.
• Long-term reputation: IP warming is an investment in long-term sender reputation, laying the groundwork for consistent inbox placement post-warmup.

Key considerations

• Strategic planning: Develop a detailed IP warmup schedule that accounts for your target daily volume, list size, and engagement levels. This plan should be flexible to adapt to real-time deliverability feedback.
• Subscriber behavior: Understand your subscribers' existing email consumption habits. If they expect daily emails, maintaining that pattern during warmup with increasing volume can be effective without causing fatigue, as explored in best practices for email frequency and volume management.
• List quality: Ensuring a clean, engaged list from the start is non-negotiable. Sending to unengaged or invalid addresses can quickly land your new IP on a blocklist (or blacklist), which you can check using our blocklist checker.
• Feedback loops: Leverage ISP feedback loops to monitor complaint rates and quickly remove recipients who mark your emails as spam, which is crucial for maintaining a good sender reputation.

Key findings

• Systematic volume increase: Documentation generally defines IP warming as sending low volumes initially and then gradually increasing them over time until target volume is reached.
• Reputation building: The primary goal of IP warming is to build a strong, trustworthy sending reputation with Internet Service Providers (ISPs).
• Engaged audience priority: Most documentation advises beginning the warm-up process by sending to the most engaged segments of your subscriber list.
• Duration variability: The duration of an IP warm-up can vary, but generally spans several weeks to months, depending on the volume and nature of the mail.

Key considerations

• Clean list hygiene: Ensure your mailing list is clean and free of invalid or risky addresses from the start. Tools for email validation are often recommended, as mentioned by Kickbox.
• Consistent sending: Maintain consistent sending practices throughout the warm-up, including frequency and content types, to help ISPs accurately profile your sending behavior.
• Monitoring and adaptation: Continuously monitor deliverability metrics such as bounces, complaints, and opens. Adjust your schedule or content as needed based on these signals. For instance, Twilio SendGrid offers guidance on this.
• Authentication setup: Ensure all email authentication protocols, such as SPF, DKIM, and DMARC, are correctly configured and aligned before beginning the warm-up process.