Does sending high-spam emails from a shared IP negatively impact other campaigns, and should they be isolated?
Michael Ko
Co-founder & CEO, Suped
Published 18 Apr 2025
Updated 19 Aug 2025
6 min read
The question of whether sending emails with high spam complaint rates from a shared IP address negatively impacts other campaigns on the same IP is a critical concern for anyone managing email deliverability. My gut feeling, like many, often leans towards isolating such campaigns, but the reality is nuanced.
When multiple senders use the same IP address, their individual sending behaviors contribute to the overall reputation of that IP. This shared reputation directly influences how mailbox providers like Gmail and Outlook perceive all mail originating from it. Therefore, if one sender on a shared IP consistently sends emails that generate high spam complaints, it can indeed drag down the reputation for everyone else.
The ripple effect of poor sending
An IP's reputation is a major factor in email deliverability, determining whether your messages land in the inbox, the spam folder, or are rejected entirely. When you share an IP, you're essentially sharing your sender reputation with others. If one campaign on that IP (even if it's yours) performs poorly, it can lead to reduced inbox placement for all other campaigns using that same IP, regardless of their individual quality.
This collective reputation means that if a high-spam campaign exists on a shared IP, it can lead to the IP (and by extension, your other campaigns) being flagged by spam filters. This might result in temporary blockages or even inclusion on a permanent blacklist. Understanding how email blacklists work is crucial in this context. You can learn more about IP reputation and how to improve it.
Mailbox providers constantly monitor sending behavior, and a sudden spike in spam complaints or bounces from a shared IP will quickly trigger their filters. This can lead to a broad negative impact on all domains using that IP, even those with excellent sending practices otherwise. It's a key reason why what a shared IP address means for deliverability is so important.
Understanding shared versus dedicated IPs
The choice between a shared and a dedicated IP often comes down to your sending volume, consistency, and the nature of your email content. Shared IPs are generally suitable for senders with lower, more sporadic volumes, as the collective sending of many users helps to maintain a stable reputation. Dedicated IPs, on the other hand, give you complete control over your reputation, but demand consistent, high-volume sending to warm and maintain their positive standing. For more details, consider when to use dedicated versus shared IPs.
It is not uncommon for organizations to send different types of emails. For example, some campaigns might be transactional (like order confirmations) and others might be promotional marketing emails. The deliverability expectations for these streams can differ significantly, making the IP choice even more critical. Here is a comparison of shared versus dedicated IPs:
Shared IP
Cost: More cost-effective, typically included in Email Service Provider (ESP) plans.
Reputation: Influenced by all senders on the IP, risking deliverability if others perform poorly.
Control: Less control over your sending reputation due to other users' behavior.
Dedicated IP
Cost: Generally more expensive, requiring dedicated resources.
Reputation: Entirely dependent on your sending practices, offering full control.
Control: Full control, but requires consistent, high-volume sending to build and maintain trust.
Choosing your IP strategy
Deciding between shared and dedicated IPs involves a careful evaluation of your email sending volume, consistency, and the type of content you send. There's no one-size-fits-all answer, and the best choice depends on your specific needs and resources. Always consider the potential impact on your sender reputation.
When to consider isolation
If you have campaigns that consistently generate high spam complaints, isolating them to a separate IP (whether another shared IP pool or a dedicated one) is a strategy worth considering. This separation can protect the reputation of your other, healthier campaigns, preventing them from being caught in the crossfire of poor sending practices. This is particularly relevant for businesses that send both transactional and marketing emails.
However, simply isolating a low-volume, high-spam campaign to its own IP isn't a magic bullet. Low-volume sending, especially with poor engagement metrics, can struggle to build and maintain a good reputation on a new, dedicated IP. Mailbox providers expect consistent, healthy sending volumes to trust an IP. If your problematic campaign has very low volume and high spam rates, moving it to a new, un-warmed dedicated IP could lead to even worse deliverability for that specific stream.
Before isolating, assess the volume of the problematic campaign. If it's very low, the risk of it plummeting on a new IP is high. Instead of immediate isolation, focus on improving the quality of the campaign, cleaning the list, and ensuring proper authentication. Remember, the goal is not just to isolate the problem, but to solve it. It's also important to manage how sharing IP ranges affects deliverability.
Risks of isolating low-volume, high-spam campaigns
Isolating a low-volume email campaign that consistently generates high spam complaints to its own dedicated IP can be risky. Without sufficient, consistent positive sending volume, the new IP may fail to build a positive reputation, leading to even poorer deliverability for that specific campaign. This is often referred to as losing the "economy of scale" that shared IPs provide.
Protecting your sender reputation
Beyond IP isolation, consistently focusing on core deliverability best practices is paramount. This includes maintaining a clean and engaged email list, implementing proper email authentication protocols like SPF, DKIM, and DMARC, and sending relevant, valuable content. Google's own email sender guidelines emphasize user engagement and compliance.
Regularly monitoring your email performance metrics, such as open rates, click-through rates, bounce rates, and spam complaint rates, can provide early warnings of reputation issues. This proactive approach allows you to identify and address problems before they escalate and affect your overall email program. You can also monitor for what happens when your IP gets blocklisted.
Ultimately, a strong sender reputation is built on trust and consistent good practices. Whether you're on a shared IP or a dedicated one, adherence to these principles will be the primary driver of your long-term email deliverability success. You can learn about DMARC, SPF, and DKIM as foundational authentication methods.
Proactive reputation management
Maintaining a healthy sender reputation requires ongoing effort. Focus on acquiring subscribers who genuinely want your emails, cleaning inactive contacts, and sending engaging content. Regularly review your deliverability metrics to identify and mitigate potential issues before they negatively impact your IP reputation.
Views from the trenches
Best practices
Maintain separate IP addresses for different email streams, especially if some have higher complaint rates.
Consistently monitor spam complaint rates and bounce rates for all campaigns, isolating problematic ones.
Ensure strong email authentication (SPF, DKIM, DMARC) to build and maintain domain trust.
Regularly clean your email lists to remove inactive or disengaged subscribers.
Segment your audience to send highly relevant content, reducing the likelihood of spam complaints.
Common pitfalls
Ignoring high spam complaint rates from specific campaigns on a shared IP, hoping it won't affect others.
Moving a low-volume, high-spam campaign to a new dedicated IP without proper warming or volume to sustain its reputation.
Failing to implement proper email authentication, which can lead to emails being marked as spam.
Sending inconsistent volumes or having long gaps between sends, which can harm IP reputation.
Not reacting quickly to mailbox provider feedback or blocklist listings, allowing issues to escalate.
Expert tips
For senders struggling with low deliverability, isolating problematic email streams is a sound strategy.
Email providers, like Oath/Verizon, have become very sophisticated at discerning good mail from bad, even on the same IP.
Microsoft's email filtering can be inconsistent and challenging, requiring continuous monitoring and adaptation.
Consider a dedicated IP only if your email volume exceeds 30 million emails per month to maintain a healthy reputation.
If moving a low-volume campaign to a dedicated IP, be aware that poor complaint rates can severely impact its standing.
Marketer view
Marketer from Email Geeks says that emails with a higher frequency of being marked as spam will likely undermine the deliverability of the good emails over time, limiting their ability to get through.
2019-04-09 - Email Geeks
Expert view
Expert from Email Geeks says that Oath and Verizon have shown strong capability in selectively delivering good and bad mail from the same IP addresses for years. However, Microsoft's filtering can be very unpredictable.
2019-04-09 - Email Geeks
Key takeaways for IP management
In conclusion, sending high-spam emails from a shared IP address unequivocally has a negative impact on other campaigns using that same IP. It compromises the overall IP reputation, potentially leading to reduced inbox placement and even blocklist (blacklist) appearances for all senders.
While isolating high-spam campaigns to separate IPs is a sound strategy to protect your main sending reputation, it requires careful consideration of the problematic campaign's volume and the associated risks. Ultimately, the most effective approach combines strategic IP management with a steadfast commitment to email best practices, ensuring your messages consistently reach the inbox.
Outlook perceive all mail originating from it. Therefore, if one sender on a shared IP consistently sends emails that generate high spam complaints, it can indeed drag down the reputation for everyone else.
