What is the best approach for warming up an IP address for email sending?

Key findings

• Consistency is key: Align your warm-up sending frequency with your intended long-term sending schedule to set accurate expectations with ISPs.
• Start small: Begin with a low volume of emails daily, typically less than 5,000, and gradually increase it by 10-20% for the first few weeks.
• Segment strategically: Prioritize sending to your most engaged and active subscribers during the initial warm-up phase to generate positive engagement signals.
• Monitor closely: Keep a close eye on deliverability metrics, including bounce rates, complaint rates, and inbox placement, to adjust your sending strategy as needed. Google Postmaster Tools can be very helpful.

Key considerations

• Content diversity: Ensure you have enough unique content for each send during warm-up to avoid sending repetitive emails to the same recipients, which can lead to disengagement.
• Throttling: Implement hourly throttling if possible, sending to your best recipients first to maximize initial positive engagement.
• IP vs. domain: While warming an IP, remember that domain reputation also plays a significant role in deliverability.
• ISP-specific nuances: Be aware that some ISPs, like Microsoft/Hotmail, can be more challenging during warm-up and may require extra vigilance.
• Automated solutions: Consider if your chosen ESP or CDP offers automated warm-up features to streamline the process.

Key opinions

• Mirror future sending: Send during warm-up as you intend to send post-warm-up to set proper expectations for mailbox providers.
• Avoid content repetition: Always have new and unique content for each send during the warm-up period to prevent subscriber annoyance and disengagement.
• Flexible frequency: If your typical send cadence is not three times a week, do not feel compelled to follow that specific recommendation; stick to your usual schedule while gradually increasing volume.
• Leverage engaged subscribers: Segment your audience to prioritize sending to highly engaged users initially, as their positive interactions provide strong reputation signals.
• Throttling strategies: Consider hourly throttling and spreading sends throughout the day to avoid triggering aggressive filtering by ISPs.

Key considerations

• Managing large lists: For very large databases, splitting highly engaged segments across multiple days during warm-up can prevent content repetition without slowing down the process significantly.
• Vendor advice: Be cautious of overly generic warm-up schedules provided by vendors, as they may not align with best practices for building a strong sender reputation.
• Tooling limitations: Standard ESPs might lack the granular controls needed for advanced segmentation and throttling required for complex warm-up strategies.
• Microsoft challenges: Hotmail (Microsoft) is frequently cited as a particularly difficult ISP during the warm-up phase, requiring careful management.
• Platform capabilities: Consider investing in CDPs or platforms that offer flexible workflows for segmentation, throttling, and robust reporting to support your warm-up efforts. More on dedicated IP warm-up best practices.

Key opinions

• Gradual introduction: Warm-up is about slowly introducing your sending domain and IP to email filters, transferring volume from existing setups to the new one incrementally.
• Prioritize positive engagement: Always send to highly engaged recipients first, especially those who actively seek out or move emails from spam, as their interactions are crucial for initial reputation building.
• Realistic content: Use the actual content you plan to send long-term for warm-up, as this provides a true representation of your future sending behavior to filters.
• Progressive volume ramp-up: Start with a very small volume (e.g., <5,000 emails/day), increasing by 10-20% daily for the first week, then doubling volumes after 2-3 weeks of consistent, positive performance.
• Modern warm-up: IP warm-up has become somewhat easier over the past five years due to better internal ISP tooling and automated warm-up features from some ESPs.

Key considerations

• Yahoo monitoring: Pay close attention to Yahoo during warm-up; receiving a TSS04 error code is a strong indicator that you are increasing your sending volume too quickly.
• Microsoft challenges: Microsoft (Hotmail/Outlook.com) can be particularly difficult and unpredictable for new IPs, often requiring careful management and patience during warm-up.
• Segmentation importance: Effective segmentation and creation of individual lists are crucial for precise control over who receives emails during warm-up. This is key to a good IP warm-up strategy.
• Avoid over-warming: For smaller lists, a protracted warm-up period is unnecessary. If your full list size is comparable to volumes typically sent after just a week of warm-up, it might be more efficient to send directly.
• Monitor deliverability: Regularly check your IP against email blocklists during the warm-up to identify any issues quickly.

Key findings

• Gradual volume increase: IP warm-up requires sending small volumes of email initially and then systematically increasing the volume over time.
• Reputation building: The primary purpose of warm-up is to build a positive sender reputation with ISPs, enabling emails to reach the inbox rather than spam folders.
• Engaged audience focus: Start by sending to your most engaged subscribers who are likely to open and click, as their positive interactions contribute significantly to reputation.
• Scheduled progression: Develop a structured warm-up schedule plan based on your sending goals and monitor it diligently.

Key considerations

• Automated solutions: Some platforms offer automated IP warm-up features that can streamline and optimize the process.
• Domain vs. IP warm-up: In many cases, warming up your domain effectively warms up associated IPs, as domain reputation is a key factor. For further reading, see how to warm up an IP or subdomain.
• Initial volume targets: Initial daily send volumes may vary by ISP, for example, around 5,000 for Gmail and 20,000 for Microsoft in the first three days.
• Engagement signals: Positive engagement signals, such as opens and clicks, are vital indicators to ISPs that your emails are valued by recipients. More on this topic in our article, how to warm up new IP addresses.