When a mid-sized e-commerce company switched from a shared IP to a dedicated IP, they expected immediate improvement in deliverability. Instead, their emails started landing in spam at higher rates than before. They'd made a classic mistake: getting a dedicated IP without the volume to support it.
The IP had no sending history. To Gmail and Microsoft, it was a blank slate—and blank slates are treated with suspicion. The company had traded the established (if shared) reputation of their email provider's IP pool for an unknown quantity that needed months of warming.
The dedicated vs shared IP decision is one of the most misunderstood choices in email infrastructure. Neither option is universally better; the right choice depends entirely on your specific situation.
How IP reputation works
Every IP address that sends email develops a reputation based on what's been sent from it. ISPs track bounce rates, spam complaints, spam trap hits, and engagement metrics. This history determines whether emails from that IP reach the inbox.
With a shared IP, you're pooling reputation with other senders. Your email provider routes messages from many customers through the same IP addresses. Everyone's behavior contributes to the collective reputation. If the pool is well-managed and other senders behave well, you benefit from their good behavior. If someone in the pool sends spam, everyone suffers.
With a dedicated IP, the reputation is yours alone. Every email sent from that IP is your email. Good behavior builds your reputation; bad behavior damages only you. There's no one else to blame—and no one else's good reputation to ride on.
The case for shared IPs
Shared IPs make sense for most senders, particularly those with lower or inconsistent volume.
The biggest advantage is inherited reputation. Good email providers carefully manage their shared IP pools, monitoring for abuse and removing bad actors quickly. The pool has established history with ISPs—it's a known quantity. When you start sending, you're not starting from zero.
Shared IPs also handle volume fluctuations gracefully. If you send 1,000 emails one week and 50,000 the next (maybe you had a big product launch), the shared pool absorbs this variation. The overall pool volume stays relatively stable even if individual senders spike.
For low-volume senders, shared IPs are often the only practical option. IP reputation requires consistent sending to maintain. If you're sending a few hundred emails per week, you can't sustain a dedicated IP's reputation on your own. The IP would go "cold" between sends, and ISPs would treat it with increasing suspicion.
The risk with shared IPs is neighbor behavior. If another sender in the pool gets compromised or starts sending spam, the IP reputation suffers, and your deliverability drops even though you did nothing wrong. Good providers mitigate this through monitoring and quick response, but the risk never disappears entirely.
The case for dedicated IPs
Dedicated IPs make sense for high-volume senders who want complete control over their reputation.
The primary advantage is isolation. Your reputation is entirely in your hands. If deliverability drops, you know the cause is something you did—not a random neighbor's spam campaign. This makes troubleshooting straightforward and gives you full control over recovery.
Dedicated IPs also provide consistency. You're not subject to reputation fluctuations caused by other senders. If you maintain good practices, your reputation stays stable. This predictability matters for businesses where email deliverability is critical.
For very high-volume senders, dedicated IPs can actually improve deliverability. ISPs recognize consistent, high-volume senders as established entities. A dedicated IP sending millions of emails monthly with good metrics builds a strong reputation that shared pools can't match.
The challenges with dedicated IPs are real though. You need sufficient volume—typically at least 100,000 emails per month, and ideally more—to maintain warm reputation. You need consistent sending; long gaps let the IP go cold. And you need to manage warming carefully when starting out.
Volume requirements
The volume question is crucial and often underestimated.
IP reputation decays without activity. If you send heavily for a month, then nothing for two months, then try to send heavily again, ISPs will be suspicious. The IP has gone cold. You'll need to warm it again, which means slow ramp-up and potentially degraded deliverability during the process.
For a dedicated IP to make sense, you typically need:
Consistent volume of at least 100,000 emails per month. Some providers suggest higher thresholds—200,000 or even 500,000—for optimal dedicated IP performance. Below these levels, you're better off with shared IPs.
Regular sending cadence. Daily sending is ideal. Weekly can work. Monthly is pushing it. If you only send quarterly newsletters, a dedicated IP will struggle to maintain reputation between sends.
Predictable patterns. Sudden spikes still cause problems even with dedicated IPs. If your volume varies dramatically, you need either multiple dedicated IPs (scaling up and down as needed) or acceptance that spikes will temporarily hurt deliverability.
The warming process
Whether shared or dedicated, new IPs need warming. But dedicated IPs require more careful attention because you can't lean on pool reputation.
Warming means gradually increasing send volume over weeks, starting with your most engaged recipients. The goal is to generate positive signals—opens, clicks, replies—that establish the IP as a legitimate sender.
A typical warming schedule might look like: Week 1, send 500 emails per day. Week 2, increase to 1,000. Week 3, 2,500. Week 4, 5,000. Continue doubling weekly until you reach your target volume. The exact numbers depend on your total volume and risk tolerance.
During warming, monitor metrics obsessively. Watch for bounce rate increases, spam complaints, or deliverability drops. If you see problems, slow down or pause. Pushing through warning signs just damages the IP further.
Warming a dedicated IP typically takes 4-8 weeks for moderate volumes, longer for very high volumes. This timeline should factor into your planning. If you need to send a million emails next month and you're starting with a fresh IP today, you have a problem.
Multiple IPs and segmentation
Large senders often use multiple dedicated IPs, segmenting traffic by type.
A common pattern separates transactional and marketing email. Transactional emails (password resets, order confirmations) typically have high engagement and low complaints. Marketing emails have more variable engagement and higher complaint risk. Keeping them on separate IPs prevents marketing problems from affecting transactional deliverability.
Some senders segment further: separate IPs for different customer segments, different product lines, or different engagement levels. Sending to highly engaged users from one IP and re-engagement campaigns from another protects your best reputation from your riskiest sends.
This segmentation adds complexity. More IPs means more warming, more monitoring, more management. But for large senders, the isolation benefits often justify the overhead.
Making the decision
Here's a practical framework for choosing:
Choose shared IPs if you send fewer than 100,000 emails per month, if your volume is inconsistent or seasonal, if you're just starting out and don't have established sending patterns, or if you want simplicity over control.
Choose dedicated IPs if you send more than 100,000 emails per month consistently, if you have the resources to manage warming and monitoring, if you need isolation from other senders' behavior, or if you're in an industry where deliverability is business-critical.
Consider a hybrid approach if you have mixed needs. Use shared IPs for lower-volume or variable sending, dedicated IPs for high-volume consistent streams. Many email providers support this flexibility.
Don't upgrade to dedicated IPs just because it sounds more professional. A poorly managed dedicated IP performs worse than a well-managed shared pool. The "dedicated" label doesn't automatically mean better deliverability—it means more responsibility.
Frequently asked questions
Can I switch from shared to dedicated IP later?
Yes, but plan for a warming period. Your new dedicated IP starts with no reputation, regardless of how long you've been sending on shared IPs. Budget 4-8 weeks for warming before expecting full deliverability.
What if someone else previously used my dedicated IP?
Dedicated IPs from reputable providers are typically cleaned before reassignment. However, residual reputation (good or bad) can linger. Check blacklists and monitor closely during initial sending. If you inherit a bad reputation, you may need to warm more carefully.
Do dedicated IPs cost more?
Usually yes. Email providers typically charge extra for dedicated IPs—anywhere from $20 to $100+ per month per IP. Factor this cost against the benefits for your specific situation.
How many dedicated IPs do I need?
Start with one unless you have specific segmentation needs. Each IP needs sufficient volume to maintain reputation. Spreading thin volume across multiple IPs is worse than concentrating it on one. Add IPs as volume grows or segmentation needs emerge.