How does sharing IP ranges affect email deliverability and how can I manage IP reputation for different clients?

Key findings

• Shared reputation: Any attribute of an email, including the IP address, carries a reputation. When IPs are shared, elements of this reputation are inherently shared among all email streams using those IPs. This can lead to a 'lowest common denominator' effect where one sender's poor practices pull down the reputation for everyone.
• Foundational impact: IP reputation serves as a foundational layer for your email program. Domain reputation and content quality build upon this foundation. If the IP reputation is compromised, it can undermine the effectiveness of even well-maintained domains and content.
• Subdomain limitation: While using different subdomains for each client helps in isolating domain reputation, the shared IP range means that issues at the IP level can still impact all associated subdomains.
• Blocklist risk: If one sender on a shared IP address engages in spammy practices, the entire IP address can become blacklisted (or blocklisted), severely affecting the deliverability of all other legitimate senders using that IP.

Key considerations

• Client segmentation: Consider segmenting your IP ranges based on client reputation or sending volume. High-volume or high-risk clients might benefit from their own dedicated IP ranges to mitigate cross-contamination of reputation.
• IP pooling: Implement IP pooling strategies. This allows you to group IPs based on performance or client type, enabling you to manage deliverability more granularly and isolate potential issues. This is especially relevant if you manage email for multiple clients as an agency.
• Monitoring: Continuously monitor the deliverability and reputation of each IP pool. Tools and practices for monitoring are essential to identify and address issues promptly before they escalate. An in-depth guide to factors that impact IP reputation can provide valuable insights.
• Throughput settings: Adjust connection and throughput settings for different IP pools to minimize the likelihood of blocks. This granular control can help stabilize deliverability for all clients.

Key opinions

• Deliverability impact: Senders sharing an IP address can experience deliverability issues if another sender using the same IP engages in undesirable practices, as the IP reputation is shared.
• Shared reputation: When using shared IP addresses, you share the same IP reputation with other senders, meaning all users can affect it. This can lead to a situation where your email deliverability is subjected to the lowest common denominator.
• Blacklisting risk: If a user on a shared IP engages in spammy practices, the entire IP address can become blocklisted, negatively affecting the sender reputation for everyone on that IP. This can lead to your emails being put on a blocklist (or blacklist).
• Benefit for low volume: Shared IP addresses can be beneficial for senders with lower email volumes or those new to email marketing, as the shared reputation (if managed well by the provider) can help avoid the initial cold-start problem of warming a new dedicated IP.

Key considerations

• Dedicated IP consideration: For higher volume senders or those who require more control over their reputation, a dedicated IP provides improved reliability and deliverability, as your sending behavior is the sole determinant of its reputation.
• Sender behavior: Regardless of IP type, maintaining good sending practices such as list hygiene, relevant content, and managing engagement is paramount. This includes avoiding spam filters and high complaint rates.
• Provider management: When using shared IPs, it is critical to choose an email service provider (ESP) that actively manages its shared IP pools to ensure consistent, high-quality sending from all users, thus protecting the shared reputation.
• Separating streams: If you send different types of emails (e.g., marketing vs. transactional), consider if separate IPs or IP pools would be beneficial to isolate their reputations. More information on shared IP addresses can help in making this decision.

Key opinions

• Shared impact: Any attribute of an email has a reputation tied to it, and by sharing IPs, elements of IP reputation are shared between email streams. The degree of impact on deliverability depends on the overall health of the entire sending program.
• Reputation hierarchy: IPs can be considered the foundation of an email program, with domain reputation building on top of that, and content layered over the domain. This hierarchical view helps visualize how issues at the IP level can affect everything above it.
• Reputation is global: IP reputation is tied to the IP address itself, not just the domains or subdomains. If that IP gets a bad reputation, it affects all senders using it, even if their individual practices are good. This includes the possibility of the IP being listed on a major blocklist.
• Importance of positive sending: An IP address that consistently sends high-quality, relevant emails with strong recipient engagement is far more likely to maintain a positive reputation, leading to better inbox placement.

Key considerations

• Pool management: Setting up IP pools (and VMTAs if using specific MTAs like PowerMTA) is crucial for managing shared IP ranges effectively. This allows for segmentation of senders and isolation of reputation issues.
• Avoiding degradation: It is vital to ensure that the lowest performing IP pool does not become too degraded, as this will 'trash' the deliverability of everyone else on that pool. Constant vigilance and prompt action are required.
• Technical configuration: Different connection and throughput settings can be configured for each IP pool to reduce the likelihood of blocks and improve overall deliverability. This fine-tuning is a key aspect of advanced IP management.
• Domain vs. IP reputation: While this article focuses on shared IPs, understanding the distinction between IP and domain reputation is crucial for a holistic deliverability strategy, especially for businesses with business partnerships that involve shared infrastructure.

Key findings

• Shared reputation model: Documentation from major ESPs often states that IP reputation is shared among all senders utilizing a common IP pool. This means good or bad sending practices from one user affect everyone.
• Mitigation through management: ESPs employ various strategies to mitigate the risks of shared IPs, such as monitoring for abuse, isolating problematic senders, and maintaining a high-quality sending environment. Users are often advised to adhere to best practices.
• Scalability for low volume: Shared IPs are frequently recommended for new senders or those with low volume, as the collective sending of many users can help maintain a warm IP reputation that an individual sender might struggle to build alone.
• Transparency: Official guides highlight the difference between shared and dedicated IPs, making it clear that shared IPs involve a collective reputation, while dedicated IPs give senders full control and responsibility over their reputation.

Key considerations

• Understanding IP pools: Familiarize yourself with how your ESP manages IP pools. Services like Twilio SendGrid, for example, explicitly mention shared IP pools and their impact on deliverability.
• Abuse monitoring: Rely on your ESP's internal monitoring and abuse detection systems for shared IPs. These systems are designed to identify and remove problematic senders to protect the overall pool reputation.
• Compliance requirements: Adhere strictly to your ESP's acceptable use policy and best practices. Non-compliance can lead to suspension or removal from shared IP pools, impacting your ability to send emails.
• Transitioning: Documentation often advises considering a transition to dedicated IPs as sending volume grows or when specific reputation control is required. This often involves an IP warming process.