Does Gmail prioritize domain or IP reputation, and how does IP warming apply?

Key findings

• Integrated approach: Gmail considers both domain and IP reputation in tandem. It's not an either/or scenario; both contribute to the overall sender score.
• Domain importance: Domain reputation, particularly tied to strong authentication like DKIM and SPF alignment, plays a critical role in how Gmail perceives a sender.
• IP warming necessity: When transitioning to new IP addresses or a new email service provider (ESP), IP warming is essential to gradually build a positive reputation for the new sending infrastructure, even if your domain reputation is already established.
• Resource warming: Google employees have clarified that warming applies to all new sending resources, including the DKIM 'd=' domain, SPF domain, '5322.from' domain, and the sending IP (along with its rDNS domain).

Key considerations

• Holistic view: Do not treat domain and IP reputation as separate entities; they are interconnected components of your overall sender trustworthiness. Understanding the difference between IP and domain reputation is critical.
• Strategic warming: Implement a careful IP and domain warming strategy, especially when making significant changes to your sending infrastructure. This helps in building a positive sender reputation.
• No perfect test: Due to the complex, non-laboratory nature of email ecosystems, obtaining definitive experimental evidence for Gmail's exact weighting of factors is practically impossible. Rely on best practices and observed trends.

Key opinions

• Domain emphasis: Many marketers believe Gmail primarily focuses on domain reputation, often leading to assumptions that existing domain authority might negate the need for IP warming.
• IP warming skepticism: Some question the necessity of traditional IP warming for Gmail if their domain reputation is already strong or if they are moving to a new ESP with a solid shared IP reputation.
• Observed fluctuations: Even with good domain practices, marketers sometimes observe temporary delivery issues or 'tempfails' when introducing new IPs, suggesting that IP reputation is still being assessed.
• Cautious approach: Despite assumptions, the prevailing sentiment is to proceed with caution and implement warming strategies for new IPs/domains to avoid deliverability setbacks.

Key considerations

• Warming is universal: Regardless of Gmail's specific algorithms, warming up new IPs and domains is a fundamental best practice for all mailbox providers to establish trust. This is particularly true when you transfer reputation with a new ESP.
• Monitor performance: Pay close attention to deliverability metrics, such as inbox placement and bounce rates, when migrating or introducing new IPs. Tools like Google Postmaster Tools can help with monitoring IP warming success.
• Segment audiences: When warming, consider segmenting your audience and gradually increasing send volumes to highly engaged users first to build positive signals.

Key opinions

• False dichotomy: Experts dismiss the idea that Gmail solely prioritizes one reputation type over the other. Both IP and domain reputation are crucial and interconnected.
• Tuple as reputation bucket: The most effective approach is to consider a combination of factors, or a 'tuple' (e.g., sending IP, sending domain, `5322.From` domain), as the holistic bucket used to track reputation.
• IP reputation is always in the mix: There's no doubt that Gmail incorporates IP reputation into its filtering decisions. Any suggestion otherwise is misleading.
• Warm up new resources: Transitioning to new IPs explicitly requires warming up all associated new resources, including various domains involved in authentication and the IP itself.

Key considerations

• Comprehensive warming: A robust warming strategy should encompass both IP and domain elements. This includes ensuring proper domain warming on existing IPs and vice versa.
• Long-term health: While domain reputation is increasingly important, neglecting IP health can still lead to deliverability issues, including being listed on a blocklist or blacklist. Consistently monitoring your domain and IP reputation is essential.
• No shortcuts: There are no shortcuts to building good sending reputation. It requires consistent good sending practices, proper authentication, and careful warming processes for any new sending resources. Learn more about Gmail's sender requirements.

Key findings

• Multi-factor assessment: Official documentation from various sources suggests that modern email filtering systems use a combination of factors, including IP reputation, domain reputation, content, and user engagement, to determine inbox placement.
• Authentication's role: Documentation often emphasizes the importance of email authentication protocols (SPF, DKIM, DMARC) as they directly build and contribute to a domain's reputation and authenticity.
• Warming for new infrastructure: Guidelines from ESPs and industry bodies consistently recommend warming up new sending IPs and domains to build a positive sending history with ISPs.

Key considerations

• Trust building: Even with a strong domain, a new IP lacks a sending history. Warming helps establish a record of legitimate sending behavior from that IP, building trust with recipients' mail servers.
• Consistency is key: Maintain consistent sending volumes and positive engagement metrics from both your domain and IP to nurture your overall sender reputation. This prevents issues like your emails going to spam.
• Reputation is dynamic: Sender reputation is not static. It is continuously evaluated based on various signals. This means continuous monitoring and adaptation are necessary. Refer to the evolution of email deliverability for more.