Is a warm up period necessary when migrating to a new ESP with the same sending domain and address?
Matthew Whittaker
Co-founder & CTO, Suped
Published 20 Apr 2025
Updated 16 Aug 2025
7 min read
Migrating to a new Email Service Provider (ESP) can seem like a straightforward process, especially when you plan to keep your existing sending domain and email address. Many marketers assume that because their domain reputation is already established, a warm-up period might not be necessary. However, this assumption often leads to deliverability issues.
The reality is that even with the same domain, your emails will be originating from a completely new set of IP addresses. Internet Service Providers (ISPs) and mailbox providers primarily assess sender reputation at the IP level, in addition to the domain level. Changing your ESP means changing the underlying infrastructure responsible for sending your emails, which in turn means starting fresh with the reputation of those new IPs.
A proper warm-up process allows you to gradually build trust with mailbox providers, demonstrating that you are a legitimate sender with consistent sending patterns. Without it, you risk triggering spam filters, landing on a blocklist (or blacklist), and severely impacting your email deliverability rates.
Why warm-up is essential, even with the same domain
While your domain carries a significant portion of your sender reputation, it’s not the only factor. When you switch ESPs, you're not just moving your contact list, you're also moving to new sending IP addresses, new DKIM keys, and potentially a new envelope sender domain, even if your 'From' address remains the same. Each of these elements contributes to how mailbox providers like Google and Microsoft assess your sending behavior.
The new IP addresses have no sending history, so they have no established reputation. Mailbox providers will be wary of high volumes of email coming from previously unknown or inactive IPs. This is why a gradual warm-up, slowly increasing your daily sending volume over time, is crucial. It helps to build a positive sending history for these new IPs.
Furthermore, while your primary sending domain remains constant, your DKIM signature will change with the new ESP. This new signature is another signal that ISPs will evaluate. A smooth transition requires aligning all these technical aspects, including DMARC, SPF, and DKIM records, to avoid being flagged as suspicious. Failing to warm up can lead to your emails being directed to the spam folder, or even result in your new IPs or domain being placed on an email blocklist (or blacklist).
Shared vs. dedicated IPs: The warm-up difference
The need for a warm-up period is particularly pronounced when migrating to dedicated IP addresses, as these IPs start with no reputation. However, even when moving to shared IP addresses, a warm-up is still advisable, albeit often less intensive. While shared IPs already have an established reputation, your sending patterns on them are new and can influence how your specific sending domain is perceived.
Dedicated IP warm-up
When you use dedicated IP addresses, you are solely responsible for building and maintaining their reputation. This requires a carefully planned, gradual increase in sending volume, often over several weeks, to prove to ISPs that you are a trustworthy sender.
Full control: Your sending practices directly impact your IP reputation.
Longer warm-up: Typically requires a more extended and structured warm-up schedule.
Higher risk/reward: Great reputation if managed well, but poor practices can severely impact deliverability.
Shared IP warm-up
Shared IP addresses already have a collective reputation built by all senders using them. While this offers some protection, your individual sending patterns from your domain on these IPs are still new and need to be established to maintain strong deliverability.
Shared responsibility: Reputation influenced by other senders on the same IP.
Faster warm-up: Often quicker as the IP has a pre-existing reputation, but still necessary.
Domain reputation focus: More emphasis shifts to your domain's sending behavior and authentication. Find out more about IP warming with shared IPs.
Regardless of whether you're on shared or dedicated IPs, the general principle remains: gradually introduce your new sending infrastructure to mailbox providers. This measured approach helps them categorize your emails as legitimate and expected traffic, rather than a sudden, suspicious burst.
Crafting your warm-up plan
A successful warm-up plan involves more than just increasing volume. It requires strategic audience segmentation and consistent monitoring. Here's a general approach:
Start small: Begin by sending to your most engaged subscribers first. These are the contacts most likely to open, click, and not mark your emails as spam, which sends positive signals to ISPs.
Gradual increase: Slowly increase your daily sending volume over a period of days or weeks, depending on your total list size and previous sending patterns. Consider how to manage sending from your old ESP during migration.
Monitor engagement: Pay close attention to open rates, click-through rates, bounces, and complaint rates. Any sudden dips in engagement or spikes in complaints are red flags.
DNS records: Ensure your SPF, DKIM, and DMARC records are correctly configured for your new ESP. Incorrect setup can severely damage your ability to deliver emails. Here's a typical DKIM record example for a new ESP:
Example DKIM recordDNS
default._domainkey.yourdomain.com IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDnQ..."
Even with the same sending domain, your DKIM will likely change, as it’s tied to the ESP’s signing keys. This is a critical component of authentication that ISPs scrutinize. Refer to guidance on warming up existing domains when using new DKIM.
Monitoring your sender reputation
Effective monitoring is crucial during and after your ESP migration. You need to keep a close eye on various metrics and indicators to ensure your sender reputation remains healthy and your emails continue to reach the inbox. Ignoring these signs can lead to deliverability problems that are much harder to fix later on.
Deliverability metrics: Track open rates, click rates, bounce rates, and spam complaint rates closely within your new ESP. Look for any significant deviations from your historical performance.
ISP feedback loops: Ensure you have feedback loops set up with major ISPs (e.g., Gmail, Yahoo, Outlook) to receive notifications about spam complaints. Address these immediately.
Blocklist monitoring: Regularly check if your new sending IPs or domain have landed on any major email blocklists (or blacklists). Being listed can severely impede your ability to reach inboxes.
The duration of the warm-up period varies based on your sending volume, list quality, and engagement. For a volume of 15,000 emails per day, a warm-up period of 2-4 weeks, starting with highly engaged segments, is a reasonable estimate. This allows mailbox providers to observe your consistent, positive sending patterns before you reach full volume.
Views from the trenches
Best practices
Gradually increase email volume by sending to your most engaged subscribers first to build positive signals for new IPs.
Ensure all DNS records, especially DKIM, SPF, and DMARC, are correctly configured for the new ESP.
Monitor deliverability metrics like open rates, click-through rates, and complaint rates closely.
Utilize ISP feedback loops and blocklist monitoring to catch and address issues quickly.
Common pitfalls
Assuming an existing domain reputation eliminates the need for any IP warm-up.
Cutting over all email volume at once, leading to sudden spikes in sending from new IPs.
Neglecting to configure new DKIM keys or other authentication records for the new ESP.
Failing to segment lists by engagement, sending to unengaged contacts too early in the warm-up.
Expert tips
Even for shared IPs, a gradual warm-up builds confidence with mailbox providers.
Reputation is a combination of many data points, and changes require rebuilding trust for the new components.
Focus on positive engagement during warm-up to demonstrate legitimate sending practices.
Be patient, a smooth transition pays off in long-term deliverability.
Expert view
Expert from Email Geeks says a warm-up will definitely be needed due to new IPs, new DKIM, and likely a new envelope domain. For a volume of 15k emails per day, it should be a quick warm-up if good practices are followed.
2023-07-06 - Email Geeks
Marketer view
Marketer from Email Geeks says they live by the rule of 'better safe than sorry,' and warming up a little bit cannot harm deliverability.
2023-07-07 - Email Geeks
Ensuring a smooth transition
In conclusion, even when migrating to a new ESP with the same sending domain and address, a warm-up period is almost always necessary. While your domain's established history provides a strong foundation, the new underlying IP infrastructure and updated authentication methods (like DKIM) require a gradual introduction to maintain trust with mailbox providers. This proactive approach helps prevent deliverability issues, keeps your emails out of the spam folder, and avoids getting listed on a blocklist or blacklist.
Prioritize sending to your most engaged subscribers during the initial phases, meticulously monitor your email performance, and ensure all your DNS records are correctly configured. By taking these steps, you can ensure a seamless transition and safeguard your sender reputation, ensuring your messages continue to reach their intended recipients effectively.
