What is a shared IP address and how does it affect email deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 29 Apr 2025
Updated 19 Aug 2025
6 min read
When you send an email, it originates from an IP address. This IP address is a crucial factor in how mailbox providers, like Gmail and Outlook, perceive your email's trustworthiness. A shared IP address means that your emails, along with those of other senders, are all routed through the same set of IP addresses. This setup is common, especially when using an email service provider (ESP), as it allows for efficient management of sending infrastructure.
The core concept behind a shared IP address (or shared IP pool) is resource efficiency. Instead of each sender requiring their own unique IP address, multiple senders collectively use a pool of addresses. This can be beneficial for those with lower sending volumes or new senders, as it allows them to leverage the pre-warmed reputation of the shared pool. However, it also introduces a shared responsibility for that reputation, which can have significant implications for email deliverability.
The impact on email deliverability
A shared IP address directly impacts email deliverability because the sending reputation is communal. When you share an IP, your email deliverability is influenced by the sending practices of everyone else using that same IP address or pool. If another sender in the pool engages in spammy behavior, such as sending unsolicited emails or experiencing high bounce rates, it can negatively affect the collective IP reputation, potentially leading to your legitimate emails being flagged as spam or even blocklisted.
Mailbox providers and internet service providers (ISPs) maintain sophisticated systems to track the reputation of IP addresses. They monitor metrics like spam complaints, bounce rates, and engagement. If a shared IP address accumulates a poor reputation due to the actions of one or more senders, all emails originating from that IP can suffer. This means your carefully crafted marketing campaigns or critical transactional emails could land in the spam folder, or be rejected outright, through no fault of your own.
The challenge with shared IPs lies in the lack of direct control over your sending environment. While ESPs typically strive to manage their shared pools and isolate bad actors, there's always an inherent risk. This is why it is important to understand how shared IP pools and sending domains impact your email sender reputation.
Advantages and disadvantages of shared IP addresses
Shared IP addresses come with distinct advantages, particularly for new senders or those with inconsistent email volumes. They can be a cost-effective solution, as the overhead of managing IP reputation is largely handled by your ESP. Many providers pre-warm their shared IPs, meaning they have an established, positive sending history, allowing you to start sending with decent deliverability from day one without the need for a lengthy IP warm-up period.
However, the disadvantages can be significant. The shared reputation is a double-edged sword: while you benefit from others' good behavior, you also suffer from their bad. If someone else on your shared IP sends spam or experiences high complaint rates, your emails could be negatively impacted. This can lead to your messages being routed to the spam folder, experiencing delayed delivery, or even outright rejection by mailbox providers. For some context, you can read more about when to use dedicated versus shared IP addresses.
Pros of shared IPs
Cost-effective: Generally included with most ESP plans, no extra cost for a dedicated IP.
Instant reputation: Benefit from the pre-warmed, established reputation of the IP pool.
Managed by ESP: ESPs handle the monitoring and maintenance of the IP's reputation.
Ideal for low volume: Suitable for senders with small or infrequent campaigns.
Cons of shared IPs
Shared reputation risk: Poor sending practices by others can harm your deliverability.
Less control: Limited ability to mitigate issues caused by other senders.
Blocklisting potential: Higher chance of ending up on a blacklist (or blocklist) due to others' actions.
Volume sensitivity: Difficult to scale high volume or inconsistent sending without risking reputation.
Managing deliverability on a shared IP
If you're using a shared IP, it's crucial to adopt robust sending practices to protect your own deliverability. This includes maintaining a clean email list, avoiding sending to unengaged subscribers, and ensuring your content is relevant and valuable. Even though you share the IP, your individual sending habits still play a significant role in how mailbox providers assess your sending domain. Managing sending volume for larger email campaigns on a shared IP is particularly important to prevent issues.
One effective strategy is to continuously monitor your email deliverability metrics. Keep an eye on your open rates, click-through rates, bounce rates, and spam complaint rates. If you notice a sudden drop in deliverability or an increase in complaints, it could be an indication of issues with the shared IP, possibly due to another sender's behavior. Regular monitoring helps you detect these issues early and take corrective action, such as adjusting your sending volume or contacting your ESP.
Additionally, ensure that your email authentication protocols like SPF, DKIM, and DMARC are correctly configured. These protocols help mailbox providers verify that your emails are legitimate and haven't been tampered with. Even on a shared IP, strong authentication signals can help distinguish your legitimate traffic from potentially problematic senders in the same pool. You can always check if you can use DMARC with shared IP addresses.
Views from the trenches
Best practices
Maintain a clean and engaged subscriber list to minimize bounces and complaints, which are critical for IP reputation.
Segment your audience and tailor your content to ensure relevance, improving engagement and reducing spam reports.
Implement strong email authentication (SPF, DKIM, DMARC) to prove your legitimacy, even on a shared IP.
Regularly monitor your email deliverability metrics, like open rates, clicks, and complaint rates, to detect issues early.
Common pitfalls
Sending to old, unengaged, or purchased lists, which leads to high bounces and spam traps.
Ignoring spam complaints or low engagement rates, as these signal poor sending practices.
Not warming up a new list, even on a shared IP, which can still cause issues.
Over-sending or sending inconsistent volumes, which can negatively impact shared IP reputation.
Expert tips
Leverage the ESP's reputation management: Shared IPs mean the ESP works to keep the IP clean, which benefits you.
Focus on domain reputation: While IP reputation is shared, your domain's reputation is entirely yours to control.
Monitor shared IP health: Use external tools to check if your shared IP is on any public blocklists.
Communicate with your ESP: If you see issues, reach out to them for insights into the shared IP's performance.
Marketer view
Marketer from Email Geeks says that transactional emails are familiar, but shared IP marketing is a new ballgame.
2021-09-29 - Email Geeks
Expert view
Expert from Email Geeks says that a shared IP address means many different companies use the same IP.
2021-09-29 - Email Geeks
Summary of shared IP impact
Shared IP addresses are a fundamental part of the email sending ecosystem, especially for businesses leveraging ESPs. While they offer benefits like lower cost and easier entry into email marketing, they also introduce the challenge of a shared reputation. Understanding how this shared environment impacts your deliverability is key to navigating the complexities of email marketing effectively.
For most senders, particularly those with consistent, moderate email volumes, shared IPs can work well, provided you maintain excellent sending hygiene. However, for high-volume senders or those with very sensitive deliverability needs, considering a dedicated IP address might be a better fit. The choice ultimately depends on your specific sending profile, volume, and risk tolerance.
Regardless of your IP setup, proactive monitoring and adherence to email sending best practices are non-negotiable for achieving strong email deliverability. Staying informed about your sending reputation and promptly addressing any issues will help ensure your messages consistently reach the inbox.
