What is the best IP warmup strategy for small send volumes when switching ESPs and using shared IPs?
Michael Ko
Co-founder & CEO, Suped
Published 26 Jul 2025
Updated 15 Aug 2025
7 min read
When switching Email Service Providers (ESPs) and dealing with small email send volumes on shared IPs, the question of an IP warm-up strategy often arises. Many assume a full-scale IP warm-up is always necessary, but this isn't always the case, especially for low-volume senders using shared infrastructure.
The goal of IP warming is to gradually build a positive sending reputation with Internet Service Providers (ISPs) and mailbox providers. This process helps them recognize your sending patterns as legitimate, reducing the likelihood of your emails landing in the spam folder. However, on shared IPs, much of the underlying IP reputation is managed by the ESP, as you are part of a pool of senders.
This guide will walk you through the optimal strategy for warming up your sending infrastructure when moving to a new ESP, focusing specifically on situations with smaller send volumes and shared IP usage. We'll cover everything from appropriate daily volumes to DMARC configurations.
Shared vs. dedicated IPs: what to know
For senders with low volumes, using a shared IP (or shared IP pool) is often the recommended approach. Shared IPs distribute email traffic from multiple senders across the same IP addresses. This means the collective sending habits of all users on that shared IP contribute to its reputation.
The primary advantage is that the ESP maintains the overall health and reputation of the shared IP. If you're a small sender, you might not generate enough consistent volume to maintain a dedicated IP's reputation effectively. Dedicated IPs require significant and consistent sending to establish and maintain a good standing with mailbox providers.
Warm-up: Less critical for the IP, but essential for the sending domain.
Crafting your warm-up schedule
For small send volumes on shared IPs, your warm-up target volume should align with your normal sending patterns, not your total list size. If you rarely send more than 5,000 emails per day, and your highest daily send is 50,000, your warm-up should aim for this typical volume rather than your entire 80,000 subscriber list. Over-warming to an unnaturally high volume, only to drop back, can negatively impact your sender reputation, as ISPs expect consistent volume.
While a 30-day warm-up is a common guideline for dedicated IPs, it's often overkill for low volumes on shared IPs. For a normal daily volume of around 5,000 emails, a one to two-week ramp-up period should suffice. The key is to gradually introduce your new sending pattern to mailbox providers without sudden spikes.
Monitor your deliverability metrics closely during this period. Keep a keen eye on bounce rates and complaint rates. If you see an increase in soft bounces or spam complaints, slow down your sending volume and investigate the issue. This iterative process allows you to build trust organically. For more information on this, check out our guide on IP warming strategies and email volume scaling.
Example small volume warm-up schedule
Day 1: 100 emails
Day 2: 200 emails
Day 3: 400 emails
Day 4: 800 emails
Day 5: 1,600 emails
Day 6: 3,200 emails
Day 7: 6,000 emails
This schedule allows for a gradual increase while remaining within a manageable daily volume. You can adjust the daily increments based on your observed performance, but doubling daily is a common starting point for low volumes.
Managing ESP migration and DMARC
When migrating ESPs, it's generally best to halt sending from your old ESP once you begin warming up your new subdomain and shared IP. Continuing to send from both simultaneously can confuse mailbox providers about your primary sending source and pattern. The transition should be as clean as possible.
One critical aspect during this migration is your DMARC configuration, especially when introducing a new subdomain. If your subdomain's DMARC policy is set to p=reject from the start, this can be risky. An aggressive policy like p=reject tells mailbox providers to bounce emails that fail DMARC authentication. If there are any misconfigurations or alignment issues during your initial warm-up, legitimate emails could be rejected.
It is advisable to start with a p=none policy and ensure your rua tag is configured to receive DMARC reports. This allows you to monitor authentication failures without impacting deliverability. Once you're confident that your emails are consistently passing DMARC, you can gradually move to a more restrictive policy, such as p=quarantine or p=reject. Setting up DMARC monitoring from day one is essential to identify and fix any authentication problems quickly.
DMARC for your subdomain
Start with p=none: Change your DMARC policy for the new subdomain to p=none to avoid rejections during warm-up. This is crucial for a smooth transition, as outlined in our simple DMARC examples.
Configure RUA reports: Add a rua tag with an email address or a DMARC monitoring service to receive aggregate reports. For example: rua=mailto:reports@yourdomain.com.
Monitor reports: Regularly check DMARC reports for authentication failures (SPF or DKIM) or unexpected sending sources. Address any issues promptly. This is critical for improving your overall email domain reputation.
Revert to p=reject (cautiously): Once mail is consistently passing DMARC and you have a stable sending pattern, you can consider changing the policy back to p=reject if that aligns with your security needs. Our article on safely transitioning your DMARC policy provides more detail.
Continuous monitoring and adaptation
The primary domain's DMARC configuration will not directly impact your new subdomain if you are sending all marketing and transactional emails from the new subdomain. DMARC applies to the domain in the 5322.from address of the email. However, resolving any DMARC issues on your primary domain is still good practice for overall domain health and security.
Ongoing monitoring is vital even after the initial warm-up period. Mailbox providers' filters learn your normal sending volume and pattern. Any drastic, sudden increases in volume (e.g., an order of magnitude increase) can trigger closer scrutiny from filters, regardless of prior warm-up efforts.
Ensure you have Google Postmaster Tools set up for your sending domain. While it won't provide real-time IP monitoring for shared IPs, it offers valuable insights into your domain's reputation, spam rates, and delivery errors, especially with DMARC record checking. Regularly reviewing these dashboards will help you detect and address potential deliverability issues before they escalate.
Views from the trenches
Best practices
Warm up based on your normal send pattern, not the total list size, to avoid misleading mailbox providers.
For small send volumes on shared IPs, a warm-up period of 7-14 days is usually sufficient, not a full month.
Start your new subdomain's DMARC policy at p=none and transition to p=reject only after consistent successful sends.
Common pitfalls
Over-warming to a volume significantly higher than your typical sends, which can lead to deliverability issues once volume drops.
Maintaining active sending from your old ESP during the new ESP's warm-up, causing confusion for mailbox providers.
Setting an aggressive DMARC policy (p=reject) for a new subdomain before confirming consistent DMARC passes, risking bounced emails.
Expert tips
If you have varied sending patterns, use your normal higher volume for warmup, and understand that spikes will always be scrutinized.
Automated warm-up features from your ESP can be helpful, but still break up lists and monitor manually.
For transactional emails, ensure those are migrated carefully and any DMARC issues are resolved to avoid interruptions.
Expert view
Expert from Email Geeks says to warm up based on your normal send pattern, not the total list, because the point is to get mailbox providers familiar with your new IP.
2021-02-26 - Email Geeks
Expert view
Expert from Email Geeks says that a 30-day warm-up is a good general guide, but for a tiny volume like 5k/day, you could easily compress that into 14 days if desired.
2021-02-26 - Email Geeks
Conclusion
For small send volumes when switching ESPs and using shared IPs, the warm-up strategy is less about the IP and more about building your domain's reputation and familiarizing mailbox providers with your new sending patterns.
Focus on a shorter, consistent warm-up period that mirrors your typical daily send volume. Implement robust authentication protocols like DMARC from day one, starting with a relaxed policy (p=none) and diligent monitoring. By carefully managing your transition and continuously observing your deliverability metrics, you can ensure a smooth migration and maintain a strong sender reputation.
