How do you warm up a new sending domain on an existing warmed IP address?
Michael Ko
Co-founder & CEO, Suped
Published 15 Apr 2025
Updated 15 Aug 2025
5 min read
When you've been sending emails from a mature, warmed-up IP address, you've already established a strong foundation of trust with mailbox providers. This means your sending infrastructure has a good reputation, indicating that you're a legitimate sender and not a source of spam. The IP address has a history of consistent, positive sending behavior, which is crucial for overall deliverability.
However, the introduction of a new sending domain, even on an existing warmed IP, brings a fresh set of challenges. While the IP's reputation is solid, the domain itself is an unknown entity. Mailbox providers assess domain reputation independently, and without a sending history, your new domain will initially be viewed with caution. This is where a strategic domain warm-up becomes essential to ensure your emails reach the inbox and maintain your sender credibility.
Why domain reputation matters, even with a warmed IP
Domain reputation is a critical factor in email deliverability, separate from your IP address reputation. Think of your IP as the post office and your domain as the return address on your envelope. Even if the post office (IP) is reputable, if the return address (domain) is unfamiliar or has no history, the mail carrier (mailbox provider) will still scrutinize it.
Mailbox providers, especially large ones like Microsoft and Gmail, extensively track domain-level metrics. These metrics include spam complaints, bounces, direct unsubscribes, and importantly, positive engagement such as opens and clicks. A new domain lacks this crucial historical data, making it appear suspicious if high volumes of email are sent too quickly.
The goal of domain warming is to gradually build trust with these providers by demonstrating consistent, positive sending behavior from your new domain. This process assures them that you are a legitimate sender and helps prevent your emails from being flagged as spam or rejected. Understanding your email domain reputation is key.
Core differences between IP and domain warming
While you're leveraging an already warmed IP address, it's important to differentiate between IP warming and domain warming. They address different aspects of your sender identity and reputation.
IP warming
Focus: Building trust at the network level for the dedicated IP address.
Goal: To show mailbox providers that the IP sends legitimate email traffic consistently.
Method: Gradually increasing email volume over time, sending to highly engaged subscribers first.
Impact: Affects the overall acceptance rate of emails originating from that IP address.
Domain warming
Focus: Building trust at the domain level, tied to your brand identity.
Goal: To show mailbox providers that your specific sending domain is trustworthy and not associated with malicious activity.
Method: Gradually increasing volume of emails sent from the new domain, focusing on engagement metrics.
Impact: Affects inbox placement, potentially bypassing spam folders even if the IP is clean.
Even with a seasoned IP, your new domain needs to earn its own reputation with mailbox providers. This is because email authentication protocols like SPF, DKIM, and DMARC are all tied to the domain. While your IP might be known, the association of that IP with a new, unproven domain can still raise red flags. It’s a combined assessment that dictates your deliverability.
The key to successfully warming up your new domain, even with a warm IP, is to start with low volumes and gradually increase them. This method, often referred to as a controlled throttle, is crucial for building trust. You'll want to prioritize your most engaged subscribers first.
A good strategy involves segmenting your audience and sending smaller batches of highly engaging content. The domain warming process relies on positive interactions. For instance, if your list is around 50,000 subscribers, you don't need to break down sends by each subscriber domain initially, but you will need to pay close attention to the major mailbox providers. Here’s a typical progression:
Week
Daily Volume
Notes
Week 1
500-1,000
Send to your most engaged segments. Focus on high open and click rates. Avoid sending on weekends.
Week 2
1,000-5,000
Broaden your audience slightly, still prioritizing engagement. Continue monitoring.
Week 3
5,000-15,000
Start sending to less active but still valid contacts. Keep an eye on spam complaints.
Week 4+
Increase volume incrementally towards your full list size, maintaining positive engagement.
Ensuring your email authentication records (SPF, DKIM, DMARC) are correctly configured for the new domain is paramount. These records tell mailbox providers that you are authorized to send emails from that domain, which is a fundamental aspect of domain reputation.
Monitoring progress and adapting your plan
Continuous monitoring is the backbone of a successful domain warm-up. You need to keep a close eye on your deliverability metrics to identify any issues early and adjust your sending strategy as needed. Key metrics include open rates, click-through rates, bounce rates (especially hard bounces), and spam complaint rates.
Monitoring tools
Leverage tools like Google Postmaster Tools for Gmail to track domain reputation, spam rates, and delivery errors. Similarly, Microsoft SNDS provides insights for Outlook/Hotmail. Regularly check your domain for blacklists (or blocklists) as well, as a new domain could quickly land on one if issues arise.
Also, monitor email service provider (ESP) reports for insights into delivery across various receiving domains. If you notice a sudden drop in engagement or an increase in spam complaints, it's a sign to slow down your sending volume for that specific domain or overall.
The duration of your domain warm-up can vary based on your list size, engagement, and the quality of your content. For a small audience, like 50,000 subscribers, the process might be quicker than for a list of millions, but the principles remain the same. Always prioritize sending to your most active users first, as their positive engagement signals trust to mailbox providers.
Views from the trenches
Best practices
Start with your most engaged subscribers on the new domain to generate positive interactions.
Segment your sending by major mailbox providers, paying close attention to Gmail, Microsoft, and Verizon Media Group.
Gradually increase email volume for the new domain over several weeks, following a controlled schedule.
Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly configured for the new domain.
Monitor deliverability metrics closely, including open rates, click-through rates, and complaint rates.
Common pitfalls
Sending high volumes from a new domain too quickly, leading to spam folder placement or blocks.
Not segmenting by engaged users during the initial warm-up phase, resulting in low engagement and poor reputation.
Failing to monitor feedback loops and adjusting sending behavior based on complaint rates.
Ignoring the independent reputation of the domain, assuming a warmed IP is sufficient.
Not properly configuring SPF, DKIM, and DMARC for the new sending domain.
Expert tips
Even if you have a warmed IP, the new domain still needs to build its own reputation with mailbox providers, especially Gmail.
Focus on domain-level reputation by prioritizing engagement and ensuring strong authentication.
A gradual increase in sending volume, often referred to as a controlled throttle, is key for new domains.
Mailbox providers like Microsoft are particularly sensitive to domain changes, requiring careful monitoring.
The warm-up process primarily applies to major ISPs, while smaller providers might not be as strict.
Marketer view
Marketer from Email Geeks says a domain change can be complicated, especially with Microsoft, and it's important to monitor how the new domain performs with Gmail and other mailbox providers by checking open rates.
2021-02-04 - Email Geeks
Expert view
Expert from Email Geeks says that warmup is fundamentally a Gmail, Microsoft, and Verizon Media Group concern, as most other places do not care as much.
2021-02-04 - Email Geeks
Maintaining deliverability with a new domain
While having a pre-warmed IP address gives you a significant advantage, it doesn't eliminate the need for domain warming when you introduce a new sending domain. Domain reputation is distinct and equally vital for deliverability.
By understanding the differences between IP and domain reputation, implementing a strategic, gradual warm-up plan, and diligently monitoring your performance metrics, you can ensure your new domain quickly earns the trust of mailbox providers. This proactive approach will help maintain your excellent deliverability and protect your sender credibility.
