How to maintain dedicated IP reputation with ISPs for email sending?

Key findings

• Evolving importance: While domain reputation is increasingly critical, IP reputation still significantly impacts deliverability, particularly with ISPs like Microsoft and T-Online.
• Sender size stratification: ISPs are improving their filtering by stratifying senders based on volume and quality, meaning dedicated IPs may not always be necessary for lower volume senders.
• Combined reputation: Multiple reputation systems (IP, domain, etc.) often work in concert. A warm domain on a warm IP may still require warming for that specific IP/domain combination.
• Historical data: ISP reactions are heavily influenced by the historical performance and trends of a mailstream. For new IPs or customers, a proper IP warming process is essential.

Key considerations

• Consistent sending volume: Maintain a steady and predictable sending schedule to build trust with ISPs. Erratic volumes can raise red flags.
• List hygiene: Regularly clean your email lists to remove inactive or invalid addresses, minimizing bounces and spam complaints.
• Engagement monitoring: Focus on positive recipient engagement (opens, clicks, replies). ISPs use engagement metrics as a strong indicator of sender reputation. Tools like Google Postmaster Tools can provide valuable insights.
• Reputation transparency: Acknowledge that ISP reputation calculations are complex and not fully transparent. Avoid making unrealistic promises to clients about deliverability. Always manage expectations, especially when transitioning email sending practices or IP addresses.

Key opinions

• Volume uncertainty: There's no universal minimum send volume for maintaining a dedicated IP's reputation, as practices vary widely among senders and ISPs.
• Historical data limitations: When moving to a new email service provider (ESP) or a new dedicated IP, historical reputation data is often inaccessible, making it challenging to predict ISP reactions.
• Ramp-up necessity: A structured warm-up plan is crucial for new dedicated IPs, regardless of prior domain reputation, to gradually build trust.
• Quality over quantity: Focusing on sending high-quality, engaged mail is more effective for building reputation than simply hitting arbitrary volume targets. This aligns with the principles of effective email campaigns.

Key considerations

• Start slow: Begin with low sending volumes and gradually increase, allowing ISPs to establish trust based on positive interactions.
• Best mail first: Send to your most engaged subscribers during the initial warm-up phases to maximize positive signals to ISPs.
• Manage client expectations: Since reputation factors are not entirely transparent, avoid making guarantees about deliverability. Instead, focus on transparent reporting and continuous improvement. This is especially important when considering platform consolidation.
• Focus on recipient interactions: User engagement (or lack thereof) provides strong signals to filters about mail quality. Mailjet suggests that by separating marketing and transactional emails on different IPs, one can ensure more crucial transactional emails maintain their standing.

Key opinions

• IP reputation's decline: Some experts assert that IP-based reputation is less critical than it once was, with filters becoming more adept at evaluating sender reputation based on size and domain.
• Quality of IP space: The overall quality of the IP block you're sending from (e.g., whether it's associated with a reputable provider) remains significant, particularly for major ISPs like Microsoft.
• Multiple reputation systems: ISPs employ various reputation systems (IP, domain, user engagement, content) that operate in concert, requiring a holistic approach to deliverability. This can complicate the process of understanding reputation interplay.
• ISP feedback: ISPs will often signal when your sending volume exceeds your established reputation, making monitoring critical to avoid blocks or throttling.

Key considerations

• Warm-up for IP/domain combinations: Even with a warm domain and a warm IP, a new combination still requires a gradual warm-up process to build specific trust with ISPs like Google.
• Prioritize user interactions: User engagement metrics, such as opens and clicks, are vital signals to ISP filters. Sending to engaged recipients first helps establish a positive reputation. For insights into engagement, consider using a comprehensive deliverability test.
• ISP-specific nuances: Warm-up is more impactful for ISPs with integrated mail servers and clients (like Gmail), as they have better visibility into engagement. Cable companies, for instance, might have less direct engagement monitoring. Understanding these differences can help inform ISP-specific warming strategies.
• Engagement definition: Defining engagement can be complex, as user behavior (e.g., moving between webmail, mobile, and thick clients) can vary widely, making consistent monitoring a challenge.

Key findings

• Gradual warm-up: Documentation consistently stresses the importance of gradually increasing sending volume on new dedicated IPs to build trust with ISPs.
• Consistency: Regular, consistent sending schedules are highlighted as crucial for maintaining a dedicated IP's reputation, avoiding fluctuations that can trigger filters.
• Monitoring: Official guides recommend continuous monitoring of IP addresses to identify and address any issues, such as being placed on a blacklist or blocklist.
• Authentication standards: Proper implementation of email authentication protocols like SPF, DKIM, and DMARC is fundamental for building and maintaining trust, as these verify sender legitimacy. For more details, explore a simple guide to DMARC, SPF, and DKIM.

Key considerations

• Dedicated IP benefits: Documentation often outlines how dedicated IPs allow senders to cultivate their own reputation, independent of others' sending behaviors, which is crucial for predictable deliverability.
• Strategic traffic separation: For senders with diverse email types (e.g., transactional vs. marketing), separating traffic onto different IPs can protect the deliverability of critical communications. This aligns with boosting overall email deliverability rates.
• Engagement signals: ISPs consider user engagement (opens, clicks, spam complaints) as key indicators of reputation. Documentation often advises senders to prioritize positive engagement to improve inbox placement. For instance, Amazon Web Services provides guidance on optimizing sending reputation with dedicated IPs.
• Dedicated IP management: Best practices for managing a dedicated IP address include careful warming, consistent volume, and continuous monitoring to ensure it is not negatively impacted.