When you send an email through an ESP, it travels from a specific IP address to the recipient’s mail server. That IP address has a reputation. And the reputation of your sending IP is one of the signals inbox providers use to evaluate your email.
You have two options: send from an IP address shared with other senders on your ESP’s pool, or send from a dedicated IP address that only you use. Each has different deliverability implications, different costs, and different management requirements.
Choosing the wrong one for your situation can hurt deliverability. Shared IPs can carry reputation damage from other senders. Dedicated IPs without sufficient volume underperform compared to the established reputation of shared pools. Understanding the trade-offs allows you to make the right choice and configure the right option correctly.
What Is a Shared IP?
A shared IP address is one that multiple senders use simultaneously. Your ESP maintains pools of IP addresses. Each pool includes many different customers’ sending activity. When you send a campaign, your emails go out from one or more IPs in your assigned pool.
The reputation of a shared IP reflects the aggregate behaviour of everyone on that pool. If you are on a pool with 500 other senders and 5 of them have spam problems, their negative signals contribute to the pool’s reputation, which your sends inherit.
Most major ESPs run multiple pools at different reputation tiers. Their highest-quality customers are on their best-reputation pools. Accounts with worse sending practices are on pools with lower reputation. Pool assignment is usually automatic based on your sending quality metrics.
What Is a Dedicated IP?
A dedicated IP address is assigned exclusively to your sending account. No other sender uses it. Every email you send from that IP builds or erodes the reputation of that IP based solely on your own sending behaviour.
Dedicated IPs are typically available as an add-on from your ESP for a monthly fee, usually $20 to $100 per month per IP. Some ESPs include dedicated IPs at their higher plan tiers.
The appeal of a dedicated IP is control. Your reputation is yours alone. A bad actor elsewhere on a shared pool cannot drag down your IP’s reputation. But the reverse is also true: a poor campaign from your own account has nowhere to hide. The full impact of a bad send lands directly on your dedicated IP’s reputation.
How Shared IP Reputation Works
Shared IP reputation is the average of all sending activity on that pool. This average can work for you or against you.
When Shared IPs Work in Your Favour
Reputable ESPs maintain their shared pools carefully. They enforce sender quality standards. Accounts that generate excessive bounces or complaints are warned and eventually removed from their high-quality pools. The result is that the best shared pools from established ESPs maintain consistently good reputations.
For a new or low-volume sender, sending from a well-maintained shared pool is better than sending from a fresh dedicated IP. The shared pool has years of positive sending history. The fresh dedicated IP has none. Inbox providers receive email from the established shared pool with the accumulated trust of all the legitimate senders on it.
Postmark is a widely cited example. Their shared pool for transactional email is strictly managed. They do not allow marketing email on the same pools as transactional email. The result is transactional email pools with excellent reputation that benefit all their customers.
When Shared IPs Work Against You
If your ESP does not maintain its pools well, or if you are assigned to a pool with other senders who have quality problems, the shared IP becomes a liability. A complaint spike from another sender in your pool can temporarily worsen inbox placement for your email even though your own campaigns are clean.
The solution is to be on a reputable ESP with well-maintained pools. Check your ESP’s documentation and community forums to understand how their pools are managed.
The Volume Threshold Where Dedicated IPs Make Sense
The central question for dedicated IP decisions is volume. Specifically: do you send enough volume to build and maintain a dedicated IP’s reputation?
An IP’s reputation is built through consistent positive sending signals. Those signals require email volume. A dedicated IP receiving 100 emails per week does not have enough activity for inbox providers to build a reliable reputation model. The result is conservative default filtering not as bad as an IP with negative history, but not as good as an established positive reputation.
The generally accepted threshold where dedicated IPs begin to pay off: approximately 100,000 emails per month, sent consistently. Below this volume, a well-managed shared pool typically outperforms a dedicated IP.
Above 100,000 monthly sends, the volume is sufficient to build meaningful reputation signals on a dedicated IP within 4 to 6 weeks of proper warm-up. Above 500,000 monthly sends, dedicated IPs are strongly recommended the volume is large enough that you want full control over the reputation signals your sends generate.
How to Warm Up a Dedicated IP Correctly
When you first get a dedicated IP, it has zero reputation history. Inbox providers treat zero-history IPs with conservative defaults. You must build a positive reputation before sending at full volume.
The Warm-Up Schedule
Week 1: 200 to 500 emails per day. Send only to your most engaged contacts — those who have clicked in the past 30 days.
Week 2: 1,000 to 2,000 per day. Expand to contacts who have clicked in the past 60 days.
Week 3: 5,000 to 10,000 per day. Continue expanding to recently engaged contacts.
Week 4: 20,000 to 30,000 per day. Include all verified, valid, active contacts.
Week 5 and beyond: Scale toward full volume at 50% increases per week while monitoring Postmaster Tools for any reputation concerns.
During warm-up, the engagement rate of your sends matters enormously. The IP is building reputation from scratch. Every positive signal (open, click, reply) and every negative signal (bounce, spam report) has a disproportionate impact because the total signal base is small.
Never send to unverified lists during warm-up. A bounce spike during warm-up can permanently limit the reputation ceiling of a new dedicated IP.
When Shared IPs Are the Better Choice
Choose a shared IP (or stay on your ESP’s default shared pool) when:
You send fewer than 100,000 emails per month. At this volume, a well-managed shared pool from a reputable ESP outperforms a fresh dedicated IP that lacks established sending history.
Your sending pattern is irregular. If you send large campaigns quarterly rather than consistently weekly or monthly, dedicated IPs are particularly problematic. Inactive IPs lose reputation over time. An IP that sends nothing for three months and then sends 200,000 emails has a warm-up problem all over again.
You are just starting a new programme. New programmes lack the consistent positive sending history to establish dedicated IP reputation quickly. Start on a shared pool and graduate to dedicated when volume and consistency justify it.
When Dedicated IPs Are the Better Choice
Choose a dedicated IP when:
You send above 100,000 to 200,000 emails per month consistently. At this volume, the investment in warm-up time pays off in full control over your reputation signals.
You have experienced quality problems on your ESP’s shared pool. If other senders on your pool have affected your delivery, a dedicated IP eliminates that risk.
You need precise control over sending patterns. Dedicated IPs allow you to separate transactional and marketing sending on different IPs with different reputations and monitoring.
You operate a high-stakes sending programme where reputation isolation is a business requirement. Financial services, healthcare communications, and government organisations often require dedicated IPs for compliance or brand protection reasons.
Managing Multiple IPs at Scale
High-volume senders often use multiple IPs simultaneously. This is common for programmes sending millions of emails per month across different email types.
Each IP should have a specific purpose. One IP for transactional email. One (or several) for marketing campaigns. Separate IPs for different product lines or brands.
Monitor each IP independently. Your reputation at Gmail is domain-level (use Postmaster Tools), but IP reputation affects other providers. Check Microsoft SNDS for each sending IP monthly. Check Sender Score for each IP monthly.
When one IP in a pool has a problem, you can pause sends from that IP and route through clean IPs while you investigate and recover. This reduces the blast radius of any reputation event.
How Domain Reputation Changes the Equation
It is important to note that Gmail’s primary reputation signal is domain-based, not IP-based. This means that for Gmail delivery specifically, the debate between shared and dedicated IPs matters less than for other inbox providers.
For Gmail, your domain reputation (visible in Postmaster Tools) is the primary filter signal. A domain with High reputation sends from either shared or dedicated IPs with similar inbox placement. A domain with Low reputation sends from either type with poor inbox placement.
Where IP reputation matters more: Microsoft Outlook, Yahoo Mail, ISP-based email (Comcast, Verizon), and smaller inbox providers that weight IP reputation more heavily than domain reputation. For these providers, the choice between shared and dedicated IPs has a more direct effect on delivery.
This is why monitoring both your domain reputation (Postmaster Tools) and your IP reputation (SNDS, Sender Score) gives a complete picture that neither alone provides.
Key Takeaways
- Shared IPs pool your reputation with other senders on the same pool. Well-managed shared pools from reputable ESPs provide good deliverability for smaller and newer programmes.
- Dedicated IPs are used exclusively by you. They provide full control over your reputation signals but require sufficient volume to build a positive reputation and proper warm-up when new.
- The volume threshold where dedicated IPs typically outperform shared pools: approximately 100,000 to 200,000 emails per month, sent consistently.
- Warm up a new dedicated IP gradually over 4 to 6 weeks. Send only to highly engaged contacts during warm-up. Never send to an unverified list during the warm-up period.
- Irregular senders should stay on shared pools. An IP that sends nothing for months and then sends a large volume has warm-up problems. Shared pool reputation is not affected by your inactivity.
- Gmail uses domain reputation as its primary signal, reducing the impact of the shared vs dedicated IP choice for Gmail delivery. IP reputation matters more for Outlook, Yahoo, and ISP-based providers.
Frequently Asked Questions
Usually when you consistently send 100,000–200,000+ emails per month and can maintain steady volume.
Yes. Poor warm-up or inconsistent sending volume can damage the IP’s reputation.
Use Microsoft SNDS and Sender Score to identify potential IP reputation issues.
Yes. Gradually move volume over 4–6 weeks instead of switching everything at once.
Usually. Shared pools provide established sending history and generally require less warm-up management.
Conclusion
The shared versus dedicated IP decision is ultimately a volume and consistency question. Smaller programmes with irregular sending benefit from the reputations of established shared pools. Larger, consistently sending programmes benefit from the control and isolation that dedicated IPs provide.
Understand which situation you are in, choose accordingly, and implement a proper warm-up for dedicated IPs and quality shared pool selection for shared. Either choice, done well, supports reliable inbox placement. Either choice, done poorly, creates avoidable deliverability problems.
