Is IP warmup necessary when moving ESPs with an engaged B2B list on a shared IP?
Matthew Whittaker
Co-founder & CTO, Suped
Published 21 Jul 2025
Updated 18 Aug 2025
8 min read
When moving email service providers (ESPs), one of the most common questions that comes up is whether IP warmup is necessary, especially when you have an already engaged list and are moving to a shared IP address. It is a nuanced topic with various factors at play, including your sending volume, list quality, and the nature of your new ESP’s shared IP pool. While the general consensus leans towards a less intensive warm-up for shared IPs, it is never entirely without consideration.
My experience tells me that even with a highly engaged B2B list and a move to a shared IP, careful monitoring and a thoughtful approach are crucial to maintaining your email deliverability. A sudden surge in volume, even of good mail, can trigger filters and potentially land your emails in the spam folder, or even lead to blocklisting (or blacklisting).
Domain reputation and shared IPs
When you are on a shared IP, your sending reputation is inherently tied to the reputation of all other senders using that same IP address. This means the ESP is responsible for managing the overall health of the IP. If you are using a shared IP, your individual sending behavior, while important, is combined with that of others. This setup can be beneficial because the ESP shoulders much of the IP reputation management, but it also means you are subject to the sending practices of other users.
However, just because you are on a shared IP does not mean you can ignore the concept of warming up entirely. Internet Service Providers (ISPs) like Google and Yahoo primarily evaluate your domain reputation. If your domain has a strong, established sending history, that positive reputation will generally follow you to a new ESP, even on a shared IP. This is a key reason why many email experts emphasize domain warm-up over strict IP warm-up for shared environments. Your domain is your consistent identifier across ESPs.
However, even with a stellar domain reputation, a sudden large volume spike from a new, unfamiliar IP can still raise flags. ISPs are wary of abrupt changes in sending patterns, as these can indicate compromised accounts or new spammers. While a full IP warm-up might not be as critical as for a dedicated IP, a gradual ramp-up of volume is always a safer approach. This allows the ISPs to observe your sending behavior and associate your trusted domain with the new (shared) IP, ensuring continued trust.
The importance of engagement and B2B considerations
Having a highly engaged B2B list is a significant advantage in this scenario. B2B recipients tend to be more forgiving than B2C, often expecting and needing professional communications. Your high open rates (30%+) and click rates (4-5%+) are strong indicators of a healthy, valuable list. This engagement acts as a positive signal to ISPs, reinforcing your sender reputation and demonstrating that your content is desired and relevant.
This positive engagement history can significantly mitigate the risks associated with moving to a new ESP, even with a new shared IP. ISPs prioritize user engagement when determining inbox placement. If your subscribers consistently open, click, and interact with your emails, it tells the ISP that your messages are legitimate and not spam. This behavioral data is powerful and can help override any initial skepticism from seeing a new sending IP.
However, it is still wise to segment your list based on engagement. Start your initial sends to your most engaged subscribers first. These are the individuals most likely to open and click, providing immediate positive feedback to the ISPs. As you gradually increase volume, you can then include less engaged segments. This strategy, often employed during any email migration, is a prudent step to ensure a smooth transition and maintain your sender reputation and email deliverability.
Practical steps for ESP migration
When migrating ESPs, even with a shared IP, several practical steps are essential. First, ensure your DNS records, including SPF, DKIM, and DMARC, are correctly configured for your new ESP. These authentication protocols are critical for proving your legitimacy as a sender, and misconfigurations can lead to immediate deliverability issues, regardless of your IP.
I recommend reviewing your SPF record to include your new ESP’s sending servers. For DKIM, ensure your new ESP provides you with the necessary records to publish. A properly configured DMARC record will then instruct receiving mail servers on how to handle emails that fail SPF or DKIM checks. Here is an example of what an SPF record might look like:
Monitoring your deliverability closely during and after the migration is non-negotiable. Pay close attention to bounce rates, spam complaints, and inbox placement. Utilize tools like Google Postmaster Tools for deliverability insights. Also check for any signs of being added to an email blacklist (or blocklist). Your ESP should also provide reports that help you track these metrics. If you see any spikes in bounces, particularly soft bounces indicating throttling, it is a sign to slow down your sending volume.
When to consider a modified warm-up
Even with an engaged B2B list and a shared IP, I would still recommend a modified warm-up approach, especially given that you are moving to a new ESP. While a full, multi-week IP warm-up might not be strictly necessary, a controlled ramp-up of your sending volume for the first few campaigns is a safe bet. This allows the receiving mail servers to recognize your sending patterns from the new shared IP without being overwhelmed.
For an 8k B2B list, this means you might not need to start at incredibly low volumes, but avoid sending the entire list on day one. A reasonable strategy would be to split your list into 2-3 batches for the first week or so. Send to your most engaged segments first, then gradually introduce the rest of your audience. This helps establish a positive sending reputation from the new shared IP within the context of your consistent domain reputation.
Remember, the goal is to demonstrate consistent, positive sending behavior to ISPs. For shared IPs, the ESP manages the overall IP reputation, but your specific domain's actions contribute significantly. If your list is clean, highly engaged, and your email authentication is strong, you significantly reduce the risk. However, no amount of engagement can fully negate the impact of a sudden, unmanaged volume spike from a new IP, even a shared one. Always err on the side of caution for a smooth transition and maintain your email deliverability rates.
Your new ESP will likely have guidelines or recommendations for migrating your list. It is always best to consult with them directly, as they understand the nuances of their specific shared IP pools and the historical sending behavior on those IPs.
IP warming strategies
There are different approaches to IP warming based on whether you are using a dedicated IP or a shared IP. Here is a brief comparison:
Dedicated IP: Requires a significant, structured warm-up process, starting with very low volumes and gradually increasing over weeks or months. You are building the IP’s reputation from scratch.
Maintain your excellent sender reputation by continuing to send highly engaged content.
Segment your list and start by sending emails to your most active subscribers first.
Ensure all your DNS records, including SPF, DKIM, and DMARC, are correctly configured for the new ESP.
Closely monitor your bounce rates, spam complaints, and overall inbox placement.
Communicate with your new ESP about their specific recommendations for migrating your list.
Common pitfalls
Sending your entire list immediately without any phased ramp-up, even on a shared IP.
Neglecting to update or properly configure your email authentication (SPF, DKIM, DMARC).
Failing to monitor deliverability metrics like bounces and spam complaints post-migration.
Assuming that a shared IP completely negates the need for any kind of sending volume management.
Not cleaning your list of inactive or invalid addresses before the migration.
Expert tips
Leverage the high engagement of your B2B list as a positive signal to ISPs.
Focus more on domain reputation than IP reputation when using shared IPs.
Even for small lists, a phased approach helps ISPs learn your sending patterns smoothly.
B2B addresses can be more resilient to initial bumps than typical B2C contacts.
Always prioritize list hygiene to avoid spam traps and reduce bounce rates.
Marketer view
Marketer from Email Geeks says a small list size like 8k and B2B nature means you are likely okay for warmth, but always monitor bounces.
2024-05-20 - Email Geeks
Expert view
Expert from Email Geeks says there is a small chance of bounces in the first campaign on that volume, depending on target mailbox providers, but a well-established domain reputation should prevent major problems.
2024-05-21 - Email Geeks
Final thoughts on IP warmup for ESP migration
In summary, while moving an engaged B2B list to a shared IP on a new ESP might not necessitate a stringent IP warm-up in the traditional sense, a cautious approach is still advisable. Your strong domain reputation and engaged audience are significant assets, but they do not eliminate the need for proper email authentication and a phased volume ramp-up during the migration. Always consult with your new ESP for their specific recommendations, as they manage the shared IP’s overall health.
By focusing on maintaining your domain reputation, correctly configuring your DNS records, and gradually introducing your sending volume, you can ensure a smooth transition and continue to achieve excellent inbox placement for your valuable B2B communications. It is about smart, calculated steps, not necessarily a full warm-up in this specific scenario.
Google and 
Yahoo primarily evaluate your domain reputation. If your domain has a strong, established sending history, that positive reputation will generally follow you to a new ESP, even on a shared IP. This is a key reason why many email experts emphasize domain warm-up over strict IP warm-up for shared environments. Your domain is your consistent identifier across ESPs.
