Why does using a shared IP affect my email deliverability?
Email problems often have nothing to do with your writing, design, or even your audience.
They start with the address your emails are sent from.
You spend days fine-tuning your campaign, crafting subject lines that feel just right, and sending it to people who genuinely want to hear from you. Everything looks perfect… until the results roll in.
Opens are low, clicks are worse, and your emails are buried in spam folders.
The reason?
Not your content, but your IP address, the digital “return address” every email carries.
If you’re using a shared IP, your sender reputation can be affected by other senders in that IP pool.
If they send spammy or irrelevant emails, it destroys the entire email deliverability ecosystem, and it can drag your campaigns down, too.
In this guide, we’ll break down how shared IPs work, why they can affect deliverability, and how to choose the right setup so your emails actually land where they belong.
What is a shared IP and how does it work?
A shared IP is basically a shared address for emails.
Instead of having your own unique “digital home,” you send from the same IP as other businesses.
Email service providers like Gmail or Outlook look at that IP’s track record to decide if your emails belong in the inbox or spam.
In such a case, your email reputation is tied to everyone else using that same IP.
If one sender has bad sending habits, like spamming, sending to fake addresses, or getting a lot of spam complaints, it drags down the reputation for everyone.
Even if your own email practices are perfect, you can still be affected.
Email providers measure IP reputation through things like bounce rates, spam complaints, sending patterns, authentication (SPF, DKIM, DMARC), and how consistent the email volume is over time.
On a shared IP, these numbers reflect the collective behavior of all senders.
Why do shared IPs exist?
Most email services use them because they’re cost-effective and easier to manage. The maintenance and setup costs are split across multiple customers, making it cheaper for everyone.
For small senders or new email programs, a shared IP with a good history can actually be a boost; it gives you instant credibility with inbox providers.
How shared IP reputation inheritance damages your email deliverability
When ESPs evaluate your emails, they don’t distinguish between you and other senders on your shared IP.
They see the IP address as a single entity and judge accordingly.
Some of the ways it can affect your email deliverability are:
#1 Shared reputation
On a shared IP, that address is used by multiple senders at the same time.
If one sender blasts spammy or low-quality emails, it damages the overall IP reputation.
ESPs (like Gmail or Outlook) judge senders heavily based on this reputation, so your emails can land in spam even if you’ve done nothing wrong.
#2 Inconsistent sending patterns
Email service providers track sending patterns over time.
A healthy pattern is steady and predictable.
On a shared IP, one company might send 10,000 emails one day and nothing the next, while another might send in small bursts.
This erratic behavior can make ESPs suspicious, potentially lowering deliverability for everyone on the IP.
#3 Higher spam complaint risk
Spam complaints occur when recipients mark an email as “spam” or “junk.” If multiple senders on a shared IP are getting high complaint rates, the ESP starts associating that IP with spam.
This affects all senders equally, so even your legitimate, permission-based emails can get caught in spam filters.
#4 Blacklisting impact
If a sender on your shared IP violates anti-spam policies, spam monitoring organizations may blacklist the IP.
Being blacklisted means emails from that IP are outright rejected or filtered into spam folders. Since all senders share the same IP, you’d also be affected even if you follow best practices.
#5 Less control over warm-up
When sending from a new IP, it needs to be “warmed up” gradually, starting with small volumes, then increasing over time to build trust with ESPs.
On a shared IP, this process isn’t in your control. If another sender suddenly sends a huge volume, it can make the IP look suspicious and trigger spam filters for everyone.
#6 Unpredictable bounce rates
Bounce rates measure how many of your sent emails fail to reach recipients.
Poor email list hygiene from another sender (sending to outdated or fake emails) can increase the IP’s total bounce rate.
High bounce rates signal to ESPs that the IP sends low-quality or risky traffic, which can push even valid emails to spam.
#7 Difficult to isolate problems
If your email deliverability drops, troubleshooting is tricky with a shared IP.
You can control your own sending practices, but you can’t see or fix what others are doing on the same IP.
This means the issue could be caused by someone else’s behavior, and you have no direct way to resolve it.
Read more: How to Find + Troubleshoot Email Deliverability Issues
Tools for checking email IP reputation
Several tools can help you assess your IP reputation status:
- Sender Score: Provides a reputation score from 0-100 for your IP address. Scores above 80 indicate a good reputation.
- Talos Intelligence: Cisco’s reputation lookup tool shows if your IP is flagged for suspicious activity.
- MX Toolbox: Checks if your IP appears on major blacklists and provides detailed reputation reports.
- Google Postmaster Tools: Shows specific data about how Gmail treats emails from your domain and IP.
- Microsoft SNDS: Provides reputation data specifically for how Outlook and Hotmail handle your emails.
Check your IP reputation monthly, or immediately if you notice deliverability problems. Early detection makes reputation issues much easier to resolve.
Dedicated IP vs shared IP: Making the right choice
Move to a dedicated IP if you send 50,000+ emails a month or face ongoing deliverability issues.
The choice isn’t just about cost, but about control, volume, and long-term strategy.
With a dedicated IP, your reputation depends solely on your sending practices, free from other senders’ mistakes.
However, it requires a steady sending volume to stay “warm.” If you send infrequently, like monthly newsletters, it could hurt deliverability.
Shared IPs can be a great option for low-volume senders when managed by a reputable provider, as the pooled reputation can help maintain inbox placement.
| Scenario | When Dedicated IPs Make Sense | When Shared IPs Might Still Work |
| Email volume | 50,000+ emails per month, sent regularly | Under 50,000 emails per month, especially if sending is irregular |
| Sending practices | Established list hygiene, authentication, and good engagement | Still building your email program, starting out |
| Reputation control | Need full control to avoid contamination from other senders | Willing to share reputation with other reputable senders |
| Campaign types | Different types (transactional, newsletters, promotional) may need separate IPs | Sending fewer, more consistent types of campaigns |
| Compliance | Required by industry/security regulations | No strict compliance requirements |
| Technical resources | Can manage IP warming, monitoring, and reputation | Limited technical resources, prefer less setup |
| Cost | Can invest in setup and maintenance | More cost-conscious; shared IPs are cheaper |
| Engagement rates | Critical to maintain high deliverability for business impact | High engagement rates reduce shared IP risks |
Hybrid approaches
| Approach | Description |
| Multiple dedicated IPs | Large senders separate IPs for transactional, newsletter, and promotional campaigns |
| Dedicated + shared | High-priority emails on dedicated IP; lower-priority on shared |
| Gradual migration | Start shared, then move to dedicated as volume and engagement grow |
| IP warming services | Platforms automate gradual volume increase while monitoring reputation |
How to choose the right IP strategy for your business
Making the right IP choice requires an honest assessment of your current situation and future plans.
Here’s a step-by-step approach:
Step 1: Audit your current sending volume and patterns. Look at your email volume over the past six months. Do you send consistently or in sporadic bursts? Are you growing steadily or plateauing?
Step 2: Evaluate your current deliverability performance. Check your inbox placement rates, bounce rates, and engagement metrics. If you’re already achieving good results with shared IPs, changing might not be necessary.
Step 3: Assess your technical capabilities. Dedicated IPs require setup, monitoring, and ongoing management. Do you have the technical expertise in-house or the budget for managed services?
Step 4: Consider your industry and audience. Some industries (like finance or healthcare) benefit more from dedicated IP control. B2B senders often see better results with dedicated IPs than B2C businesses.
Step 5: Calculate the cost-benefit ratio. Factor in not just IP costs, but setup time, management overhead, and potential deliverability improvements.
Best practices for email deliverability using any IP address type
Regardless of whether you choose shared or dedicated IPs, these practices improve deliverability:
- Maintain impeccable email list hygiene: Remove bounced addresses immediately, suppress unsubscribes promptly, and never purchase email lists.
- Implement proper authentication: Modern email platforms automatically configure SPF, DKIM, and DMARC records, ensuring proper authentication without technical complexity.
- Monitor engagement closely: Track opens, clicks, and replies to verify you’re sending relevant content to interested recipients.
- Segment your audience: Send targeted content to specific audience segments rather than blasting generic messages to everyone.
- Respect sending frequency: Find the sweet spot between staying top-of-mind and overwhelming subscribers.
- Use clear, honest subject lines: Avoid spam trigger words and misleading promises that generate complaints.
- Include easy unsubscribe options: Make it simple for recipients to opt out rather than marking your emails as spam.
Whether you use a shared or dedicated IP, SmartReach helps keep your emails landing in the inbox. With built-in IP reputation monitoring, automated list hygiene, and advanced warm-up tools, you don’t have to worry about the technical heavy lifting.
Focus on crafting great emails – SmartReach.io takes care of deliverability.
Try SmartReach.io FREE for 14 days.
Frequently asked questions
Q1: What are the cons of a shared IP address?
A shared IP’s reputation depends on all senders using it. If another sender sends spam or triggers blacklists, your deliverability may suffer. You also have less control over sending patterns and IP warm-up.
Q2: Do you mail off dedicated IPs or shared IPs?
It depends on your email volume, resources, and deliverability needs. High-volume, consistent senders often benefit from dedicated IPs, while lower-volume or new senders usually start with shared IPs.
Q3: What does sharing an IP address do?
Sharing an IP means multiple senders’ emails are routed through the same IP. This spreads both the benefits and risks of that IP’s reputation among all senders.
Q4: Why is sharing an IP address bad?
It’s not always bad, but it can be risky. If another sender behaves poorly, your emails could be flagged or blocked because the IP’s overall reputation drops.
Q5: What is one disadvantage of using a static IP address?
A static IP can be targeted more easily for attacks, and if it gets blacklisted, you may face persistent deliverability issues until the block is removed.
Q6: What is the difference between a shared IP address and a dedicated IP address?
- Shared IP: Used by multiple senders, lower cost, reputation is shared.
- Dedicated IP: Used by one sender only, more control over reputation, requires proper warm-up and management.
Q7: Is it illegal to share an IP address?
No, sharing an IP address is legal and common in hosting and email services. The key concern is managing the shared reputation.
Q8: What does it mean if someone is sharing my IP address?
It means multiple users are assigned the same public IP by their ISP or hosting provider. In the email, it indicates that your sending activity is linked with others using the same IP.
