Should I segregate sending IPs by recipient domain to improve email deliverability?

Key findings

• Limited impact: Mailbox providers like Gmail and Outlook assess sender reputation independently. Your sending reputation at one provider typically does not directly influence your reputation at another, even if you are sending from the same IP address. This means segregating by recipient domain often provides no direct deliverability benefit.
• Focus on behavior: Deliverability is primarily driven by sender reputation, which is built on recipient engagement, complaint rates, bounce rates, and adherence to email best practices across all sends. Audience segmentation based on engagement or behavior is far more impactful than IP segregation by recipient domain. For example, sending to highly engaged users can improve your deliverability for engaged users.
• Spammer tactic: Historically, this approach has been associated with spammers who use different IP pools to target specific mailbox providers, attempting to bypass blocks or maximize delivery from lower-quality IPs. It is not a recommended strategy for legitimate senders.
• Niche exceptions: In very rare, specific circumstances, such as circumventing country-level ISP throttling, a dedicated IP pool for certain regions might be considered. However, this is an advanced scenario and not a general best practice for improving overall campaign deliverability.

Key considerations

• Reputation management: Instead of segregating by recipient domain, focus on maintaining a strong, consistent IP and domain reputation across all your sending. This involves careful list hygiene, monitoring engagement, and adhering to authentication standards like SPF, DKIM, and DMARC. Learn more about maintaining dedicated IP reputation.
• Strategic IP allocation: A more common and effective strategy is to segregate IPs and subdomains based on email type, such as transactional versus marketing emails. This protects the reputation of critical transactional sends from the potential impact of marketing campaign issues. Twilio provides a comprehensive guide on best practices to improve deliverability.
• Audience segmentation: Implement audience segmentation based on engagement levels, demographics, or other behavioral data, rather than recipient domain. Tailoring content and frequency to these segments will yield better engagement and, consequently, better deliverability.
• Deliverability issues: If you're facing deliverability problems, focus on identifying the root cause. This typically involves analyzing bounce rates, complaint rates, spam trap hits, and DMARC reports, rather than resorting to complex IP segregation by recipient domain.

Key opinions

• Ineffective strategy: Many marketers believe that segmenting IPs by recipient domain is a waste of time, as mailbox providers maintain independent reputations for IPs, meaning issues at one provider typically do not spill over to others.
• Audience behavior is key: The focus should be on how different audiences interact with emails. If Gmail users are more engaged than Hotmail users, it's an audience segmentation issue, not an IP one. Segmenting by audience type and engagement improves deliverability.
• Outdated tactic: The idea might stem from historical spammer tactics where different IP pools were used to target specific ISPs or countries to avoid blocks. For legitimate senders, this is rarely beneficial.
• Simplicity is best: If there isn't a clear, identified deliverability problem that this strategy would solve, it's better to stick to simpler, proven methods to avoid over-complicating sending infrastructure without tangible benefits.

Key considerations

• Identify the actual problem: Before implementing complex IP strategies, marketers should first ascertain if a deliverability problem exists and, if so, what its specific nature is. This could be high bounce rates, low inbox placement at specific providers, or blocklisting. Tools like an email deliverability tester can help.
• Focus on content and list hygiene: Prioritize engaging content, proper email authentication (SPF, DKIM, DMARC), and diligent list cleaning. These factors have a much larger impact on sender reputation and inbox placement. Mailgun discusses domain warm-up and reputation.
• Transactional vs. marketing: A more valuable IP segregation strategy involves separating transactional emails from marketing emails, often using distinct IPs or subdomains for each type. This helps protect the deliverability of critical transactional messages.
• Consistent sending: Building a consistent sending volume from your dedicated IPs helps establish a reliable sending reputation with mailbox providers. Erratic sending patterns or unnecessary IP fragmentation can sometimes hinder this process.

Key opinions

• Misguided strategy: Experts view this approach as a misunderstanding of how mailbox providers (ISPs) evaluate sender reputation. ISPs track reputation on an IP and domain level based on overall sending quality and user engagement, not on a per-recipient-domain basis for IP segregation.
• Spam association: The practice of creating IP pools for specific recipient domains has historical roots in spammer tactics, where senders would rapidly switch IPs or content based on a seedlist to find winning combinations to bypass filters. This association makes the strategy suspicious to deliverability professionals.
• Focus on core metrics: Instead of recipient-domain IP segregation, experts advise focusing on fundamental deliverability metrics like engagement rates, complaint rates, bounce rates, and blocklist (or blacklist) presence. These are the true indicators of sending health.
• Limited legitimate use: While there might be extremely rare, specific cases (e.g., bypassing throttling by a particular country's ISP using an APNIC pool), these are exceptions and not general best practices. For large email lists, the focus remains on reputation.

Key considerations

• Understand reputation: It's vital for senders to understand that IP and domain reputation are built over time through consistent, good sending practices to an engaged audience, not through artificial segregation. Consistent positive engagement across all domains will positively influence your domain reputation.
• Segment by email purpose: If IP segregation is considered, it should primarily be to separate email streams by purpose (e.g., transactional, marketing, cold outreach) using dedicated IPs or subdomains, not by recipient domain. This is a widely accepted best practice for risk mitigation.
• Holistic deliverability: Focus on a holistic deliverability strategy that includes proper authentication (SPF, DKIM, DMARC), maintaining a clean list, monitoring feedback loops, and creating relevant content that fosters engagement.
• Avoiding blocklists: If IP segregation by recipient domain is being considered due to concerns about global blacklists, the underlying issue is poor sending practices. The solution is to fix those practices, not to try and outsmart individual mailbox providers. Regularly check if your IP is blocklisted.

Key findings

• Reputation is global: Mailbox providers primarily assess the reputation of an IP address and sending domain based on the overall quality of mail originating from them, irrespective of the specific recipient domain. A positive reputation benefits all recipients, regardless of their email provider.
• Authentication is paramount: Documentation consistently emphasizes the importance of implementing SPF, DKIM, and DMARC. These protocols verify sender identity and are critical for deliverability, far more so than complex IP segregation schemes. WebexConnect highlights that emails must pass SPF checks for deliverability.
• Content and engagement: ISPs value user engagement (opens, clicks, replies) and relevant content. Documentation encourages senders to focus on these aspects rather than on intricate IP routing by recipient domain. Bloomreach notes that larger senders should split sending across IPs, but for transactional vs. marketing.
• Subdomain usage: Some documentation advises using separate subdomains for different email types (e.g., transactional, marketing, notifications) to isolate reputation. This is a common and effective strategy, but it is distinct from segregating IPs by recipient domain. Onesignal recommends setting up multiple subdomains for different mail categories.

Key considerations

• IP warm-up: When using new IPs, documentation recommends a gradual warm-up process to build reputation. This process involves slowly increasing sending volume over time, which applies to the IP's overall sending, not specific recipient domains. Mailgun details how larger senders split sending across dedicated IPs.
• Dedicated vs. shared IPs: Documentation often guides on whether to use dedicated or shared IPs, usually based on sending volume and list hygiene. Dedicated IPs are typically recommended for high-volume senders who can maintain a consistent sending reputation, which is a broader concern than per-recipient domain segregation.
• Monitoring and feedback loops: Postmaster tools and feedback loops provided by major ISPs are designed to give senders insights into their overall sending performance, including complaint rates and reputation scores. These tools monitor aggregate IP and domain performance, reinforcing the idea of a unified reputation.
• Compliance: Adhering to legal and ethical email sending practices (e.g., CAN-SPAM, GDPR) and respecting unsubscribe requests are foundational for deliverability, regardless of IP segregation strategies. DanaConnect advises using separate IPs for transactional and marketing emails.