The startup was proud of their email practices. Clean list, engaged subscribers, proper authentication. Then their deliverability tanked overnight. Investigation revealed the cause: another sender on their shared IP had been sending spam. The IP's reputation collapsed, taking everyone on it down.
The obvious solution seems to be dedicated IPs—your own address, your own reputation, no one else's problems affecting you. But dedicated IPs come with their own challenges, and for many senders, shared IPs are actually the better choice.
Here's how to decide.
How IP reputation works
Email reputation is tied to both your domain and your sending IP address. When you send email, receiving servers check the IP's history: Has it sent spam before? What's its complaint rate? How do recipients engage with email from this IP?
On a shared IP, your reputation is pooled with other senders. Good senders lift everyone up; bad senders drag everyone down. The email service provider manages who shares the IP, ideally grouping senders with similar quality.
On a dedicated IP, your reputation is yours alone. Your sending practices determine your deliverability. No one else can hurt you—but no one else can help you either.
Dedicated IP advantages
Complete control. Your reputation depends entirely on your own practices. If you maintain good list hygiene, send relevant content, and follow best practices, your reputation reflects that.
Isolation from others. Other senders' mistakes don't affect you. If someone else on a shared IP sends spam, you're not collateral damage.
Predictable deliverability. With consistent sending practices, your deliverability is predictable. You're not subject to reputation fluctuations caused by others.
Required for high volume. At very high volumes (millions of emails monthly), dedicated IPs are typically necessary. Shared IPs can't handle the volume, and your sending would dominate the shared reputation anyway.
Some compliance requirements. Certain industries or compliance frameworks require dedicated infrastructure, including dedicated IPs.
Dedicated IP challenges
Requires volume to maintain. IP reputation needs consistent sending to stay warm. If you send sporadically or in low volumes, your IP's reputation decays between sends. Most providers recommend at least 100,000 emails per month for dedicated IPs.
Warmup required. New IPs have no reputation—they're unknown, which is treated with suspicion. You need to warm up a new IP gradually over 4-8 weeks, starting with small volumes to engaged recipients and slowly increasing.
You own all problems. If something goes wrong—a bad campaign, a list quality issue, a complaint spike—there's no buffer. The damage hits your IP directly and fully.
More expensive. Dedicated IPs cost more than shared. You're paying for exclusive use of infrastructure.
Requires expertise. Managing dedicated IP reputation requires understanding of deliverability, monitoring, and remediation. It's not set-and-forget.
Shared IP advantages
No warmup needed. Shared IPs are already warm with established reputation. You can start sending immediately at full volume.
Works for low volume. If you send 10,000 emails per month, a dedicated IP would struggle to maintain reputation. Shared IPs aggregate volume from many senders, maintaining consistent reputation.
Buffered from your mistakes. If you have a bad campaign, the impact is diluted across all senders on the IP. One mistake doesn't destroy your deliverability.
Lower cost. Shared infrastructure is cheaper. You're splitting the cost with other senders.
Managed by experts. Good ESPs actively manage shared IP pools, removing bad senders and maintaining reputation. You benefit from their expertise without needing it yourself.
Shared IP challenges
Vulnerable to others. If another sender on your IP behaves badly, your deliverability suffers. You're trusting your ESP to manage the pool well.
Less control. You can't directly influence the IP's reputation beyond your own sending. If the pool's reputation declines, your options are limited.
Reputation ceiling. On a shared IP, your deliverability is capped by the pool's reputation. Even perfect practices can't overcome a mediocre shared reputation.
Potential for inconsistency. Shared IP reputation can fluctuate as senders come and go. Your deliverability might vary even with consistent practices.
Decision framework
Choose dedicated IP if:
- —You send more than 100,000 emails per month consistently
- —You have the expertise to manage IP reputation
- —You need isolation for compliance or risk management
- —You're willing to invest in warmup and ongoing monitoring
- —Predictable, controllable deliverability is critical
Choose shared IP if:
- —You send less than 100,000 emails per month
- —Your sending volume is inconsistent or seasonal
- —You want to start sending immediately without warmup
- —You trust your ESP to manage shared pools well
- —You prefer simplicity over control
The volume threshold
The 100,000 emails per month threshold isn't arbitrary. It's roughly the volume needed to maintain IP reputation through consistent sending.
Below this threshold, a dedicated IP's reputation decays between sends. ISPs see sporadic sending from an IP and treat it with suspicion. The IP never builds the consistent positive signals that establish trust.
Above this threshold, you're sending enough to maintain warmth and build reputation. Your sending patterns are consistent enough that ISPs recognize you as a legitimate sender.
Some providers set the threshold higher (250,000+) or lower (50,000+) depending on their infrastructure and how they define "dedicated." Ask your provider what volume they recommend for dedicated IPs.
Hybrid approaches
Some organizations use both:
Dedicated for transactional, shared for marketing. Transactional email (password resets, order confirmations) is critical and typically high-volume. Marketing email is less critical and more variable. Separate IPs match the different requirements.
Multiple dedicated IPs by type. Large senders might use different IPs for different email types, isolating reputation by category. A problem with marketing email doesn't affect transactional delivery.
Graduated approach. Start on shared IPs, move to dedicated as volume grows. This avoids premature dedication while building toward eventual control.
Frequently asked questions
Can I switch from shared to dedicated IP?
Yes, but it requires warmup. You can't just flip a switch—you need to gradually shift volume to the new dedicated IP over several weeks while it builds reputation. Plan the transition carefully.
How do I know if my shared IP has problems?
Monitor your deliverability metrics. If delivery rates drop without changes to your practices, the shared IP might be the cause. Ask your ESP about the IP's reputation and whether other senders are causing issues.
Do I need multiple dedicated IPs?
For most senders, one dedicated IP is sufficient. Very high-volume senders (millions per day) might need multiple IPs to distribute load. Some senders use separate IPs for different email types to isolate reputation.
What happens if my dedicated IP gets blacklisted?
You'll need to identify and fix the cause, then request removal from the blacklist. Recovery can take days to weeks. This is why dedicated IPs require expertise—you need to handle problems yourself.