Do I need an IP warm-up when moving to a new ESP with shared IPs?
Matthew Whittaker
Co-founder & CTO, Suped
Published 20 May 2025
Updated 18 Aug 2025
7 min read
Moving to a new Email Service Provider (ESP) is a significant step for any organization. One of the most common questions that comes up during this transition is whether an IP warm-up period is necessary, especially when shifting to a new ESP that utilizes shared IP addresses. Many assume that because the IPs are shared and already have an established reputation, a warm-up isn't needed. However, the reality is a bit more nuanced than a simple yes or no answer.
While the traditional, intensive IP warm-up process primarily applies to dedicated IP addresses, your sender domain's reputation and how internet service providers (ISPs) perceive your sending patterns remain crucial, even on shared infrastructure. Gmail and other major mailbox providers continuously monitor sending behavior, and any sudden, drastic change, even on shared IPs, can trigger their spam filters.
Understanding shared IPs and reputation
When you send emails through an ESP's shared IP addresses, you are using IPs that are also used by many other senders. The ESP is responsible for managing the overall reputation of these shared IPs. They typically have sophisticated systems in place to monitor sending behavior across their user base, mitigate risks, and maintain a healthy IP reputation.
This collective management means that the IP warm-up (or ramp-up) is largely handled by the ESP itself, ensuring that new IP addresses are introduced and managed carefully. Therefore, you typically won't perform a direct "IP warm-up" in the same way you would with a dedicated IP. However, this doesn't mean you can disregard a gradual transition entirely. Your domain, even if it has a strong existing reputation, will be seen sending from a new set of IP addresses for the first time by ISPs.
A key distinction is that while the IP reputation is shared and managed by the ESP, your domain's reputation is entirely your own. Mailbox providers assess both IP and domain reputation. If your domain suddenly appears on a new set of IPs with a high volume of email, it can look suspicious, regardless of the shared IP's pre-existing reputation. This is why a domain warm-up (or careful migration) is still highly recommended.
Key takeaway
While dedicated IP warm-up protocols don't directly apply when moving to shared IPs, your domain reputation still needs careful management during migration. A gradual ramp-up is crucial to signal legitimate sending patterns to ISPs.
Why a warm-up (of sorts) is still beneficial
Even with shared IP addresses, ISPs, like Microsoft, employ sophisticated machine learning algorithms to assess sending patterns and identify potential spam. When your sending domain suddenly starts originating emails from a completely new set of IP addresses, even if they are shared, these algorithms need time to "learn" and verify that this is a legitimate change, not an unauthorized takeover or a spam operation.
Without a gradual transition, you may experience fluctuations in your deliverability metrics. This could manifest as emails landing in spam folders, delayed delivery, or even temporary blocklisting (or blacklisting) if the change is too abrupt and perceived as suspicious. While the ESP manages the IP's reputation, your domain's sending reputation is still tied to its historical behavior and how it transitions to new sending infrastructure.
The key is that the recipient's mailbox provider (e.g., Gmail, Outlook, Yahoo) needs to build trust with your domain coming from these new shared IPs. This trust is built by observing consistent, desired sending patterns. A sudden spike in volume from an unfamiliar IP range, even if shared, can be a red flag. This is why a strategic ramp-up period is still advisable, even if it's not the traditional IP warm-up.
As Twilio SendGrid explains, if you're sending lower volumes of email, you will generally send email on a shared IP, which does not require individual warm-up. However, this doesn't negate the importance of a gradual transition for your specific domain and sending habits.
Dedicated IP warming
This involves a strict, gradual increase in sending volume from a brand new, unused IP address. The goal is to build a positive sending reputation for that specific IP with mailbox providers.
Control: Full responsibility for IP reputation.
Process: Requires careful planning, daily volume increases, and monitoring.
Typical use: High-volume senders with consistent sending patterns.
Shared IP transition
This focuses on gradually transitioning your domain's sending volume to the new ESP's shared IPs. The ESP manages the underlying IP reputation.
Control: ESP manages IP, you manage domain reputation.
Process: Gradual migration of segments, focusing on engagement.
Typical use: Most senders, especially those with moderate to lower volumes.
Key considerations for migration
Even when using shared IPs, there are critical steps to take to ensure a smooth transition and maintain your sender reputation. It's not about warming up the IP, but about warming up your domain's relationship with the new IP space and validating your sending behavior.
Firstly, prioritize migrating your most engaged subscribers first. Sending to highly engaged segments from the new ESP's shared IPs will send positive signals to ISPs, helping to build trust for your domain on this new infrastructure. Avoid sending large volumes to unengaged lists early in the process. You should also ensure you bring over your suppression lists and any engagement data from your old ESP.
Secondly, ensure all your email authentication records (SPF, DKIM, DMARC) are correctly configured for the new ESP. This is fundamental for deliverability and tells mailbox providers that your emails are legitimate. You can use a free DMARC record generator to ensure proper setup. You also need to actively monitor your deliverability and blacklist status from day one to quickly identify and address any issues.
Finally, consider a phased migration. Instead of an abrupt switch, gradually shift your sending volume from the old ESP to the new one over a period of days or weeks. This allows mailbox providers to adjust to the change. This process is often called a sending ramp-up for your domain, rather than an IP warm-up.
Aspect
Action for smooth transition
Volume scaling
Start with lower daily volumes and gradually increase over a few weeks. The goal is a controlled ramp-up, not a sudden surge.
List segmentation
Begin by sending to your most engaged subscribers who are likely to open and click, providing positive engagement signals.
To ensure your email deliverability remains strong during and after an ESP migration to shared IPs, consistency and vigilance are key. A sudden increase in volume from a new set of shared IPs can temporarily impact your sender reputation, even if those IPs are generally well-regarded.
It's important to understand that while a shared IP environment takes some of the warm-up burden off your shoulders, your domain still needs to establish trust with mailbox providers from its new sending location. This requires a carefully planned ramp-up strategy for your domain, focusing on engagement and positive signals.
Always maintain good list hygiene, segment your sends effectively, and monitor your deliverability metrics closely. If you start seeing emails land in the spam folder or encountering blocklist issues, it's crucial to scale back and investigate.
Views from the trenches
Best practices
Start by sending to your most active and engaged subscribers to build initial trust with the new IPs.
Gradually increase your sending volume over several weeks, even on shared IPs, allowing mailbox providers to adapt.
Ensure your SPF, DKIM, and DMARC records are correctly configured for the new ESP to validate your emails.
Continuously monitor your deliverability and domain reputation using available tools.
Common pitfalls
Abruptly switching all sending volume to the new ESP on day one without any ramp-up.
Sending to unengaged or old lists immediately, which can generate spam complaints and bounces.
Neglecting to monitor deliverability metrics and
blocklist appearances during the transition period.
Expert tips
Consider a dual-sending approach, gradually shifting volume from the old ESP to the new one.
Focus on domain reputation and audience engagement as primary drivers of deliverability on shared IPs.
Leverage your new ESP's deliverability support team for guidance during the migration.
Pre-warm your existing domain reputation by ensuring strong engagement before the move.
Marketer view
Marketer from Email Geeks says you won't be penalized per se, but you may see fluctuations in metrics and placement as you migrate. Gmail and other ISPs will need to adjust to your domain sending from different IPs.
2023-02-21 - Email Geeks
Marketer view
Marketer from Email Geeks says some kind of warm-up process is still advised, even if not as iterative as a typical IP warm-up. You still need to be able to check your deliverability and reputations.
2023-02-21 - Email Geeks
Navigating your ESP transition
While moving to a new ESP with shared IPs might seem to negate the need for an IP warm-up, it's crucial to understand that your domain's reputation still requires a careful and phased transition. The goal isn't to warm up the IPs, which your ESP manages, but to ease your domain's new sending patterns onto those IPs.
By gradually increasing your sending volume to engaged segments, ensuring proper authentication, and diligently monitoring your deliverability, you can minimize potential disruptions and ensure your emails continue to reach the inbox effectively. This strategic approach helps mailbox providers, like Laura from Word to the Wise suggests, to recognize your legitimate sending behavior, even from a new shared environment.
