What are the best practices for email IP warm-up when switching to a new ESP?
Michael Ko
Co-founder & CEO, Suped
Published 19 May 2025
Updated 30 Sep 2025
7 min read
Moving to a new Email Service Provider (ESP) is a significant step for any business, offering new features and potentially better performance. However, one of the most critical, yet often overlooked, aspects of this transition is IP warm-up. It's not just a recommendation, but a fundamental process to safeguard your email deliverability and maintain a strong sender reputation. Skipping or mishandling this phase can lead to your emails landing in spam folders, negating any benefits of the new ESP.
The goal of IP warm-up is to gradually establish a positive sending history with Internet Service Providers (ISPs) like Gmail and Outlook. When you switch to a new ESP, you'll likely be sending from new IP addresses, whether dedicated or shared. ISPs view emails from new or unknown IPs with suspicion until they observe consistent, desired sending patterns. This initial period is critical for avoiding blocklists (or blacklists) and ensuring your messages reach the inbox. It's about building trust, one email at a time.
Understanding IP warm-up fundamentals
A successful IP warm-up is a strategic process that involves careful planning and execution. The core idea is to start with low sending volumes to your most engaged subscribers, gradually increasing the volume and diversifying your audience over several weeks. This methodical approach signals to ISPs that you are a legitimate sender sending desired content, helping you build a positive sending reputation from the ground up.
The exact duration and volume increases can vary, but the principles remain constant. For instance, Twilio SendGrid's Email Guide to IP Warm Up highlights the importance of sending low volumes initially and then slowly increasing them. This careful ramp-up allows ISPs to observe consistent sending behavior and positive engagement metrics, which are crucial for establishing trust.
Remember that IP warm-up isn't a one-size-fits-all solution. Factors like your list size, sending frequency, and the specific ESP's infrastructure will influence your strategy. Always tailor your approach, but never compromise on the fundamental principle of gradual, measured increases. You can find more detailed guidance on best practices for IP warm-up for dedicated IPs and shared IPs in other resources.
Crafting your IP warm-up strategy
When transitioning to a new ESP, a detailed IP warm-up strategy is essential. It's not enough to simply switch providers, you must actively manage the perception of your new sending infrastructure. A common schedule involves starting with a very small volume, such as 500 emails on the first day, and incrementally increasing the volume daily or every few days.
Audience segmentation: Begin by sending to your most engaged subscribers who consistently open and click your emails. Their positive engagement metrics will help build a solid foundation of trust with ISPs.
Volume increase: A typical recommendation is to increase your sending volume by 30-40% daily. Some ISPs might be more sensitive, so a 40% increase can be safer than 50%.
Consistent sending: Maintain a consistent sending schedule throughout the warm-up period. Erratic sending can raise red flags for ISPs.
Content quality: Ensure your content is high-quality, relevant, and expected by your recipients. Avoid anything that might trigger spam complaints.
Domain authentication: Always use your own domain for sending and ensure proper SPF, DKIM, and DMARC records are in place and correctly configured. This is fundamental for proving your identity and preventing spoofing.
Day
Approximate Volume
Increase From Previous Day
Target Audience
1
500-1,000
N/A
Most engaged users
2
700-1,400
~40%
Most engaged users
3
980-1,960
~40%
Most engaged users
Weeks 2-4
Gradually increasing
30-40%
Expand to less engaged segments
It’s vital to closely monitor your deliverability metrics throughout this period. Tools that offer DMARC monitoring can provide invaluable insights into how ISPs are treating your emails, helping you adjust your strategy as needed. This continuous feedback loop is what allows for a successful IP warming strategy.
Common pitfalls and how to avoid them
Even with a solid plan, it's easy to fall into common traps during IP warm-up. One major pitfall is attempting to send too large a volume too quickly. Starting with 500,000 emails on a brand new, unwarmed IP address is a recipe for disaster. ISPs will flag such sudden, high-volume sending as suspicious, likely leading to immediate blocklisting (or blacklisting) and severe damage to your sender reputation.
Recommended practices
Start with a very low volume (e.g., 500-1,000 emails) to your most engaged subscribers on day one. Gradually increase this volume by 30-40% each day, monitoring your engagement rates closely. Always use your own sending domain, authenticated with SPF, DKIM, and DMARC. This builds trust with ISPs and ensures your brand reputation is tied to your sending practices.
Risky advice to avoid
Never initiate IP warm-up with excessively high volumes, such as 500,000 emails from a cold IP. Do not use an ESP's generic or shared domain for your email sending, as this can severely dilute your brand's reputation and lead to poor deliverability. Such practices indicate a lack of understanding of fundamental email deliverability principles.
Another critical mistake is failing to properly authenticate your sending domain with your new ESP. Even if your old ESP handled DMARC, SPF, and DKIM configuration, you need to ensure these are correctly set up for your new provider. Using a new ESP's generic sending domain, rather than your own, is particularly harmful. This separates your sending reputation from your brand, making it difficult to control deliverability and inviting spoofing or phishing attempts.
Always prioritize your own domain for sending. It allows you to build and maintain your brand's unique sender reputation, which is far more valuable and controllable than relying on an ESP's potentially fluctuating shared IP or domain reputation. If an ESP suggests otherwise, it's a strong indicator to question their expertise.
Monitoring and maintaining your sending reputation
IP warm-up isn't a one-time task, it's the initial phase of ongoing sender reputation management. Post-warm-up, continuous monitoring of your email campaigns is crucial. This includes keeping a close eye on key metrics like open rates, click-through rates, bounce rates, and crucially, spam complaint rates. High complaint rates, even after warm-up, can quickly damage your newly established reputation.
Implementing a DMARC policy and actively monitoring its reports is indispensable for maintaining strong deliverability. DMARC provides crucial visibility into who is sending email on behalf of your domain, helping you identify unauthorized senders and authentication issues. Tools like Suped's DMARC monitoring can simplify this complex process, providing actionable insights from your DMARC aggregate reports. This empowers you to address potential problems before they escalate into significant deliverability issues.
Maintaining a clean and engaged email list is also an ongoing best practice. Regularly cleaning your list of inactive subscribers and invalid email addresses reduces bounces and spam complaints, further bolstering your sender reputation. A healthy list, combined with vigilant monitoring and proper authentication, sets the stage for long-term email success.
Views from the trenches
Best practices
Start with very low email volumes, as little as 500 emails on the first day, for new IPs.
Increase sending volume gradually by 30-40% daily, observing ISP acceptance and engagement.
Prioritize sending to highly engaged subscribers initially to build a positive reputation.
Ensure your sending domain is properly authenticated with SPF, DKIM, and DMARC.
Common pitfalls
Initiating IP warm-up with excessively high volumes, such as 500,000 emails on day one.
Trusting ESP advice that contradicts standard, gradual warm-up procedures.
Using a new ESP's generic or shared domain instead of your own for sending.
Failing to adequately monitor campaign performance and domain reputation.
Expert tips
A 40% daily increase in sending volume can be a safer bet with some ISPs compared to 50%.
Aim for non-existent complaint rates during warm-up to establish a strong reputation.
Always ensure your new domain is used for signing all emails during warm-up.
Consolidate sending platforms to improve deliverability and streamline warm-up processes.
Expert view
Expert from Email Geeks says starting a new IP warm-up with 500,000 emails on the first send is far too much, and the process should begin with as few as 500 emails, gradually increasing from there.
2025-01-14 - Email Geeks
Expert view
Expert from Email Geeks advises that 500K emails for the first day of warm-up is extremely high and questions the technical competence of an ESP suggesting such a volume.
2025-01-14 - Email Geeks
Achieving smooth ESP transitions
Switching to a new ESP is an opportunity to revitalize your email program, but it demands a meticulous and informed IP warm-up process. By starting with small volumes, targeting engaged subscribers, gradually increasing your sends, and ensuring your domain is correctly authenticated, you build a strong foundation for future deliverability.
Vigilant monitoring, especially through DMARC reports, will be your guiding light throughout this transition and beyond. Avoiding common pitfalls, such as sending too much too soon or relying on an ESP's generic domain, is critical. With careful planning and execution, your ESP migration can lead to improved engagement and sustained inbox placement, ensuring your messages always reach their intended audience.
The goal of IP warm-up is to gradually establish a positive sending history with Internet Service Providers (ISPs) like Gmail
and Outlook. When you switch to a new ESP, you'll likely be sending from new IP addresses, whether dedicated or shared. ISPs view emails from new or unknown IPs with suspicion until they observe consistent, desired sending patterns. This initial period is critical for avoiding blocklists (or blacklists) and ensuring your messages reach the inbox. It's about building trust, one email at a time.
The exact duration and volume increases can vary, but the principles remain constant. For instance, Twilio SendGrid's Email Guide to IP Warm Up highlights the importance of sending low volumes initially and then slowly increasing them. This careful ramp-up allows ISPs to observe consistent sending behavior and positive engagement metrics, which are crucial for establishing trust.
Leveraging tools like Amazon SES's email sending health dashboard
or Google Postmaster Tools is highly recommended. These provide valuable data directly from ISPs about your sender reputation. Additionally, proactive blocklist monitoring helps you quickly detect if your IP or domain gets listed, allowing for swift action to mitigate damage.
Implementing a DMARC policy and actively monitoring its reports is indispensable for maintaining strong deliverability. DMARC provides crucial visibility into who is sending email on behalf of your domain, helping you identify unauthorized senders and authentication issues. Tools like Suped's DMARC monitoring can simplify this complex process, providing actionable insights from your DMARC aggregate reports. This empowers you to address potential problems before they escalate into significant deliverability issues.
