Does sending high-spam emails from a shared IP negatively impact other campaigns, and should they be isolated?

Key findings

1. Reputation spillover: Poor sending practices or high spam complaint rates from one campaign can degrade the shared IP's reputation, affecting the deliverability of all other campaigns on that IP. This can lead to increased spam folder placement or even blocklisting for otherwise legitimate emails.
2. ISP sophistication: Some major internet service providers (ISPs) like Oath (Verizon Media) have advanced filtering that can differentiate between good and bad mail even from the same IP. However, this isn't universal, and other providers, such as Microsoft, may have less consistent filtering mechanisms.
3. Domain vs. IP reputation: While IP reputation is crucial, domain reputation also plays a significant role in deliverability. Even with a good domain reputation, a poor IP reputation can hinder inbox placement.
4. Isolation as a strategy: Moving campaigns with higher spam rates to a separate IP can protect the reputation of your primary sending IPs and improve overall deliverability for your high-performing emails.
5. Volume considerations: Dedicated IPs require consistent high volume to maintain their reputation. Low-volume campaigns, even those with high spam rates, may struggle more on their own dedicated IP due to a lack of economy of scale for reputation building.

Key considerations

1. Assess campaign types: Consider if the campaigns prone to spam complaints are fundamentally different in nature (e.g., marketing versus transactional, or cold outreach versus engaged subscribers). Different sending patterns and audience expectations might warrant separate IPs.
2. Evaluate volume: Before isolating, determine if the low-performing campaigns generate enough volume to sustain a dedicated IP's reputation. If not, moving them might not solve the problem and could create new deliverability issues.
3. Implement best practices: Focus on improving list hygiene, consent, and content for the problematic campaigns. Addressing the root cause of high spam complaints is always the best long-term solution, regardless of IP strategy.
4. Monitor performance: Continuously monitor deliverability metrics (inbox placement, spam complaints, bounces) for all your campaigns. This helps you quickly identify issues and decide whether IP segmentation is necessary.

Key opinions

1. Higher spam frequency impacts good mail: Marketers believe that campaigns with a higher frequency of being marked as spam will eventually limit the ability of good emails from the same IP to reach the inbox.
2. Gut feeling for isolation: Many marketers instinctively feel that 'bad' campaigns should be moved to their own dedicated IP address to prevent them from dragging down the reputation of other, better-performing emails.
3. Protecting sender reputation: If other senders on a shared IP engage in questionable practices, it can negatively affect your sender reputation, leading to higher spam rates.
4. Inconsistency on shared IPs: The performance of a shared IP can be inconsistent due to varying email sending patterns and volumes from different users, which poses a challenge for deliverability.
5. B2B specific data: Some marketers only have spam unsubscribe data from specific B2B domains like Microsoft and Oath, which can influence their perspective on shared IP impact.

Key considerations

1. Isolation as a last resort: If you cannot fix the underlying issues causing high spam complaints, isolating problematic campaigns is often seen as the best course of action.
2. Avoid mixing campaign types: Marketers generally dislike the idea of sending both general marketing and more aggressive sales marketing emails from the same IP.
3. Understand volume relativity: The definition of 'low volume' for a dedicated IP is relative and can vary based on email service providers and target domains.
4. Consider warming: If isolating to a new IP, remember that proper email warming is crucial to build a positive reputation from scratch.

Key opinions

1. ISP selective delivery: Some experts note that major mailbox providers, such as Oath (Verizon), have become very good at selectively delivering both good and bad mail from the exact same IPs, meaning isolation isn't always strictly necessary.
2. Microsoft's filtering: There is acknowledged inconsistency and unpredictability in Microsoft's email filtering mechanisms, making deliverability to these domains particularly challenging.
3. Volume is paramount: Experts stress that sending volume is crucial for maintaining a healthy IP reputation. Low volume, especially when combined with poor complaint rates, can cause a dedicated IP to struggle.
4. Dedicated IP thresholds: Some experts suggest a high monthly email volume, such as 30 million messages, as a threshold for when a dedicated IP becomes truly necessary or beneficial.
5. Risks of low-volume isolation: Moving low-volume campaigns to a dedicated IP can be fiddly and risky, even in good circumstances, as they may lose the economy of scale in reputation building.

Key considerations

1. Evaluate ISP behavior: Recognize that different ISPs handle shared IP reputation differently. While some can selectively filter, others might penalize the entire IP.
2. Monitor volume thresholds: If considering a dedicated IP, ensure your sending volume is sufficient to maintain a healthy reputation. Below certain thresholds (e.g., 300k/month), it can be difficult to sustain a good IP.
3. Not always critical to separate: While separating campaigns might feel reasonable, it's not always the end of the world if you cannot separate them, especially if you focus on overall sending quality.
4. Strategy for large campaigns: For larger email campaigns on shared IPs, it is generally recommended to manage sending volume carefully to avoid reputation dips.
5. Deciding on IP type: The choice between shared and dedicated IPs should be based on your sending volume, consistency, and the nature of your email content. Consider which IP type best suits your needs.

Key findings

1. Shared IP basics: A shared IP address is utilized by multiple senders, which means the collective sending behavior of all users on that IP contributes to its overall reputation.
2. Impact of negative practices: If even one sender on a shared IP engages in spammy behavior, it can lead to the IP being blocklisted. When an IP is blacklisted, all emails sent from it, regardless of sender, may be automatically marked as spam or rejected.
3. Marketing mail reputation: Marketing mail, often sent by other users in shared IP pools, inherently tends to lower IP reputation compared to transactional mail due to differing engagement patterns.
4. Dedicated IP suitability: Businesses sending high volumes of emails with consistent quality are typically advised to use a dedicated IP infrastructure to have full control over their sending reputation.
5. Bad IP reputation consequences: A poor IP reputation can significantly impact a sender's overall reputation, often resulting in emails being rejected by receiving servers and hurting deliverability.

Key considerations

1. Maintain list hygiene: Regardless of IP type, maintaining clean email lists and practicing double opt-in are crucial to minimize spam complaints and maintain a good sender reputation.
2. Understand IP vs. domain impact: While shared IPs can negatively impact deliverability, modern systems also weigh domain reputation. Ensuring proper authentication like DMARC, SPF, and DKIM is essential.
3. Monitor blocklists: Regularly check if your sending IP or domain has been added to any email blocklists or blacklists. Being listed can severely affect deliverability for everyone on a shared IP. Learn more with an in-depth guide to email blocklists.
4. Choosing the right IP type: The decision between a shared and dedicated IP should align with your specific email strategy, considering factors like sending volume, consistency, and content type. Consult official guides for making this choice.