Is IP warming necessary when migrating ESPs to shared IPs, and what are the best practices?
Michael Ko
Co-founder & CEO, Suped
Published 10 May 2025
Updated 15 Aug 2025
7 min read
Migrating your email sending to a new Email Service Provider (ESP) is a significant undertaking. One of the most frequently asked questions during this process, especially when moving to shared IP addresses, is whether IP warming is still necessary. The common assumption is that if the IPs are shared, they are already warmed by other senders, thus negating the need for your own warm-up period.
While it's true that shared IPs come with an established sending history and reputation, the full picture is more nuanced. Your domain's reputation, the quality of your list, and your sending practices all play a critical role in how mailbox providers (ISPs) perceive your emails, regardless of the underlying IP.
The nature of shared ips
When you use shared IP addresses, you are sending alongside other users of your Email Service Provider. This means the IP's reputation is a collective one, managed and maintained by the ESP. Reputable ESPs work diligently to keep their shared IP pools clean and in good standing with Internet Service Providers (ISPs), which often means these IPs are indeed pre-warmed to some extent.
The primary advantage here is that you're not starting from scratch with a completely cold IP. ISPs (like Amazon SES) recognize these IPs and have existing data on their sending patterns and overall reputation. This can provide a smoother transition than if you were warming a brand new, dedicated IP, where the entire reputation burden rests solely on your shoulders.
However, relying solely on the shared IP's warmth can be risky. While the IP might be fine, ISPs also evaluate the reputation of your sending domain. If your domain is new, or if its reputation changes significantly after migrating to a new ESP (even a shared IP pool), it can trigger spam filters.
Therefore, even with shared IPs, it's prudent to approach an ESP migration with a strategy that considers your domain's sending history and how the new ESP's infrastructure might affect it. This is where a more holistic view of email reputation comes into play, extending beyond just the IP address itself.
Domain reputation and migration considerations
While shared IPs reduce the direct need for IP warming, your domain's reputation is a separate, yet equally critical, factor. Mailbox providers assess both the IP and the domain when deciding where to deliver your email. A sudden spike in volume from a previously low-volume domain, even on a warm shared IP, can raise red flags.
This is why many experts still recommend a soft warm-up or gradual ramp-up for your domain, particularly when migrating a substantial list or changing sending patterns. This practice helps to build trust with ISPs under your new sending configuration. It demonstrates consistent, desired sending behavior, preventing emails from going to spam.
Starting your migration by sending to your most engaged subscribers is a best practice. These recipients are more likely to open, click, and interact positively with your emails, sending strong positive signals to ISPs. This approach helps quickly establish a positive reputation for your domain on the new ESP's infrastructure, even if the IPs are already warm. Over time, you can gradually expand your sending volume to less engaged segments.
Even with small lists, like 10,000 subscribers, a measured approach can prevent deliverability hiccups. While the IP might be seasoned, your domain is essentially starting fresh in the eyes of some ISPs, especially if they haven't seen your domain sending from this specific shared IP pool before. Think of it as introducing your brand to a new neighborhood, even if the street itself is already bustling.
Shared ip considerations
Pre-warmed: IPs already have sending history and reputation.
Shared reputation: Deliverability can be affected by other senders on the same IP.
ESP management: Your ESP actively manages the IP's standing with ISPs.
Domain considerations
New context: Your domain is sending from a new IP environment.
Individual reputation: Domain reputation is built through your sending behavior.
Engagement signals: Positive interactions are key for domain trust.
Key strategies for a successful migration
Even without a rigorous IP warming schedule, a well-planned ESP migration is essential. The goal is to ensure continuous positive engagement with your subscribers and maintain a strong sender reputation. Here are some key strategies to implement:
Prioritize list hygiene
Before migrating, clean your email list. Remove unengaged subscribers, hard bounces, and any known spam traps. Sending to a clean, engaged list is the most crucial factor for good deliverability, regardless of your IP type. This minimizes complaints and bounces, which can severely damage your domain's reputation. A healthy list is the foundation for avoiding getting blocklisted (or blacklisted).
Implement authentication standards
Ensure your DNS records for SPF, DKIM, and DMARC are correctly configured on your new ESP. Proper authentication signals to ISPs that your emails are legitimate and from an authorized sender. This is a non-negotiable step for any email program, and particularly vital during a migration. You can use a DMARC record generator to set up your DMARC. Learn more about DMARC, SPF, and DKIM.
Monitor deliverability closely
Use tools like Microsoft SNDS and Google Postmaster Tools to track your sending reputation, complaint rates, and spam trap hits. Pay close attention to early signs of trouble and adjust your sending strategy if necessary. This proactive approach helps in quickly identifying and resolving any potential deliverability issues.
Engage subscribers consistently
Consistent, relevant, and engaging content is key to maintaining a good sender reputation. Your subscribers' positive interactions (opens, clicks, replies) are powerful signals to ISPs that your emails are desired and valuable. Conversely, low engagement, high bounce rates, or increased spam complaints can quickly undermine your efforts, even on shared IPs.
Migration checklist for shared IPs
Clean your list: Remove inactive subscribers and bad addresses.
Authenticate domains: Configure SPF, DKIM, and DMARC records correctly.
Segment audience: Start with your most engaged recipients.
Monitor performance: Keep an eye on deliverability metrics and feedback loops.
Maintain engagement: Send valuable content consistently to foster positive interactions.
For a list of 10,000, you likely won't need an aggressive IP warming schedule typically associated with dedicated IPs and very large volumes. However, a thoughtful, phased approach to your domain and audience segments is still your best bet for avoiding email delivery issues and ensuring a smooth transition to your new ESP.
Day
Initial volume (highly engaged)
Maximum volume (less engaged)
Day 1-3
200-500
Segment by 90-day engagement
Day 4-7
500-1,000
Expand to 60-day engagement
Day 8-14
1,000-2,000+
Expand to 30-day engagement, then full list
Views from the trenches
Best practices
Always start with your most engaged segments to build trust quickly with ISPs.
Ensure all authentication protocols (SPF, DKIM, DMARC) are correctly configured before sending.
Monitor your deliverability metrics daily, even on shared IPs, for any anomalies.
Common pitfalls
Assuming zero warm-up is needed because IPs are shared, neglecting domain reputation.
Sending to the entire list at once, especially unengaged segments, which can lead to blocklists.
Not monitoring deliverability closely after the migration, missing early warning signs.
Expert tips
Throttle your sending speed initially, even for small lists, to observe performance.
Focus on domain warming by prioritizing positive engagement signals.
If possible, gradually introduce the new ESP by running a small portion of your sends concurrently for a short period.
Marketer view
Marketer from Email Geeks says that if you are going to a shared pool, there's generally no need to warm anything, as the IPs should already be warmed.
2020-06-18 - Email Geeks
Marketer view
Marketer from Email Geeks notes that ramp-ups are not just for IPs but also for domains and any other changes during an ESP switch. Gmail considers the overall picture, and a change in ESP can make the domain's reputation questionable.
2020-06-18 - Email Geeks
Navigating your ESP transition
Migrating to a new ESP, even when utilizing shared IPs, requires strategic planning beyond just flicking a switch. While the IPs themselves often come pre-warmed, your domain's reputation is paramount, and it needs careful nurturing in its new environment.
By prioritizing list hygiene, ensuring robust authentication, strategically ramping up your sending to engaged segments, and diligently monitoring your performance, you can ensure a smooth transition and maintain stellar deliverability. It's about smart migration practices, not just IP addresses.
