How should a sender allocate campaigns across multiple IPs when migrating from an in-house setup?
Michael Ko
Co-founder & CEO, Suped
Published 27 Jul 2025
Updated 18 Aug 2025
7 min read
Migrating from an in-house email setup to a new Email Service Provider (ESP) is a significant undertaking, especially for high-volume senders. It involves careful planning to ensure your email deliverability remains strong and avoids disruption. One of the primary challenges when you're moving your entire email infrastructure is figuring out how to best allocate your various campaigns across the new dedicated IP addresses provided by your ESP.
Consider a scenario where you're sending roughly a million emails per month, encompassing six distinct campaign types: promotional, triggered, transactional, customer service, newsletters, and re-engagement. If you have four dedicated IPs at your disposal, with one designated for transactional mail and three for promotional, determining the optimal allocation strategy is critical, particularly as you're also introducing new subdomains into the mix. This initial setup is key to maintaining or even improving your sender reputation.
The way you segment and distribute your sending volume across these IPs and subdomains can heavily influence your inbox placement. It's not just about spreading the load, but about intelligently grouping email types to manage sender reputation effectively and prevent any one campaign from negatively impacting others. This detailed approach ensures a smooth transition and establishes a healthy sending foundation.
Allocating your campaigns
When approaching a migration like this, my first step is to categorize the email streams by their nature and importance. You have transactional, triggered, and customer service emails, which are typically high-priority, expected communications. Then there are promotional, newsletters, and re-engagement campaigns, which tend to be bulkier and more sensitive to recipient engagement. The goal is to isolate your most critical email streams to protect their deliverability from the potential impacts of lower engagement campaigns.
Given your four IPs, with one for transactional and three for promotional, a clear strategy emerges. The single transactional IP should be exclusively for transactional emails, as these have the highest open and engagement rates, forming a strong reputation foundation. This separation is paramount because transactional emails are often time-sensitive and critical to user experience.
For your monthly volume of one million emails, having three dedicated promotional IPs is quite generous. Often, this volume might not necessitate that many IPs unless there are specific, nuanced sending patterns or a desire for extreme segregation. However, since you have them, we can use them strategically.
IP segregation benefits
Reputation isolation: Poor performance on one IP doesn't affect others.
ISP trust: ISPs can assign specific trust levels to IPs based on email type.
Targeted warming: Tailor your IP warming for each email stream's specific characteristics.
Promotional IP 1: Newsletters, highly engaged promotional content.
Promotional IP 2: General promotional, re-engagement campaigns.
Promotional IP 3: Reserve for testing or future growth, or consolidate.
Aligning subdomains and IP warming
For the three promotional IPs, I recommend starting by consolidating your promotional and newsletter volume onto two of them. The third promotional IP can initially remain unused or be reserved for specific, highly segmented campaigns if your volume grows significantly beyond the one million mark. For a monthly volume of one million, typically two well-managed dedicated IPs (one transactional, one promotional) would suffice for a healthy deliverability profile. However, having an extra IP provides flexibility.
Using subdomains is a best practice that complements IP allocation by allowing for further segmentation of your sender reputation. You can align subdomains with your IP assignments, for example: transactional.yourdomain.com, marketing.yourdomain.com, and newsletter.yourdomain.com. This provides a granular view of your sending reputation at the subdomain level, which is valuable for troubleshooting and optimization. It's important to understand how to manage subdomain reputation when using multiple IPs.
The critical next step after IP and subdomain allocation is warming them up. Since all four IPs and subdomains are new to your ESP, they effectively have no sending history, meaning no reputation. Warming them is a gradual process of increasing sending volume to build trust with Internet Service Providers (ISPs).
Warming the IPs and subdomains
A comprehensive guide to IP and domain warming outlines the importance of starting with highly engaged recipients and gradually expanding your audience. This helps ISPs recognize your IP as a legitimate sender. For transactional emails, you can often warm up faster due to high engagement. For promotional, a slower, more deliberate ramp-up is typically required. Review the best IP warm-up strategy for server migrations.
It's vital that the warming process for each IP is carefully managed. Do not suddenly blast high volumes. Instead, send small, consistent volumes and gradually increase them. Monitoring your deliverability rates, bounce rates, and complaint rates during this period is crucial. Any spikes in negative metrics should prompt a reduction in volume until the issue is resolved.
The length of the warming period can vary, but for a monthly volume of one million emails across four IPs, you should plan for at least 4-6 weeks, if not longer, especially for the promotional IPs. This ensures a robust reputation is built before you return to your full sending volume. This process is essential for warming a dedicated IP without interruption.
IP warming best practices
Start small: Begin with a low volume of your most engaged subscribers.
Increase gradually: Incrementally increase sending volume daily or weekly.
Segment audiences: Use your most active segments first for best results.
Monitor metrics: Keep a close eye on bounces, complaints, and engagement.
Consistency is key: Maintain regular sending patterns throughout the warming period.
Monitoring and avoiding pitfalls
Once your IPs are warmed, continuous monitoring becomes your most important task. This involves tracking various deliverability metrics, including open rates, click-through rates, bounce rates, and complaint rates. Pay particular attention to how different ISPs (Gmail, Outlook, Yahoo) are receiving your mail, as their filtering algorithms can vary.
Vigilance against being placed on a blocklist (or blacklist) is also essential. Being on a blocklist can severely impede your email deliverability, sending your messages straight to the spam folder or blocking them entirely. Regular blocklist monitoring and understanding how email blacklists actually work can help you quickly identify and address any issues. Remember, a blocklist is a list of IP addresses or domains known to send spam.
Should you find yourself on a blacklist (or blocklist), swift action is required. This often involves identifying the root cause, resolving it, and then submitting delisting requests to the specific blocklists. Maintaining a clean sending list, adhering to email authentication protocols, and providing clear unsubscribe options are proactive measures that help prevent blocklisting issues.
Final considerations for your migration
In a scenario with 1 million monthly emails and four dedicated IPs, the allocation strategy is foundational for a successful migration. Prioritize the transactional IP for critical, high-engagement emails and strategically consolidate promotional traffic across the remaining IPs. A diligent IP and subdomain warming schedule, coupled with continuous monitoring and proactive reputation management, will set you up for long-term deliverability success.
Views from the trenches
Best practices
Start with your most engaged subscribers during IP warming, regardless of campaign type.
Segment your campaigns by recipient behavior or content sensitivity (e.g., transactional vs. marketing).
Align subdomains with your IP addresses to further isolate and manage reputation.
Regularly monitor your email deliverability metrics for each IP and subdomain.
Common pitfalls
Sending high volumes on a new, unwarmed IP, which can trigger spam filters.
Mixing transactional and promotional emails on the same IP, risking deliverability for critical messages.
Ignoring negative feedback loops or spikes in complaint rates.
Failing to segment lists by engagement, sending to inactive users during warming.
Expert tips
For 1 million emails per month, two IPs (one transactional, one promotional) might be sufficient if managed well.
If you have extra IPs, consider reserving one for future expansion or for highly sensitive, targeted campaigns.
Leverage the new ESP's onboarding support and deliverability experts for guidance.
Ensure DMARC, DKIM, and SPF records are correctly configured for all IPs and subdomains.
Expert view
Expert from Email Geeks says that a total monthly volume of 1 million messages is not a high volume, especially when considering four dedicated IPs. They suggest that the client could give the transactional campaigns one IP address, and then place the remaining campaigns on another IP, making a total of two IPs. This approach would simplify the IP warm-up plan.
2021-10-21 - Email Geeks
Expert view
Expert from Email Geeks says that some ESPs tend to provide more dedicated IPs than others, and sometimes the number of IPs a client has may not accurately reflect the volume they are sending. It could be due to the ESP's policy, or simply because the client ordered more IPs than necessary.
