Is domain warming effective for boosting email deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 7 Jul 2025
Updated 16 Aug 2025
7 min read
When launching a new email program or domain, one of the most frequently discussed topics is domain warming. It's often presented as a critical first step, a rite of passage for any sender aiming for the inbox. The core idea is simple: gradually increase your email sending volume from a new domain to build its reputation with internet service providers (ISPs).
The goal is to show mailbox providers that your sending behavior is legitimate and consistent, thereby earning their trust. This trust is essential for ensuring your emails land in recipients' inboxes rather than getting filtered into spam or blocked entirely. Without a solid reputation, new domains are often viewed with suspicion, making it challenging to achieve optimal deliverability.
The foundation of sender reputation
Sender reputation is the bedrock of email deliverability. Mailbox providers, such as Google and Microsoft, assess your domain's sending history and engagement metrics to determine where your emails should land. A new domain starts with a neutral reputation, which means it has no established history of good or bad sending practices. This lack of history often triggers stricter scrutiny, leading to higher chances of emails being marked as spam or blocked.
Domain warming serves to proactively build this reputation, signaling to ISPs that you are a legitimate sender rather than a potential spammer. It involves gradually increasing your email volume, ensuring that initial sends are to highly engaged, opt-in recipients. This positive engagement helps establish a baseline of trust.
Without proper warming, a sudden surge in email volume from a new domain can immediately raise red flags with ISPs. They might interpret this as spam activity, leading to your domain being placed on a blocklist (or blacklist) and severely impacting your email deliverability. This process is crucial for establishing a solid foundation for all future email communications.
New or cold domain
No established sender reputation.
High likelihood of emails landing in spam folders or being rejected.
ISPs treat sending as suspicious due to lack of trust.
Warmed domain
Positive sender reputation built on consistent, legitimate sending.
Improved inbox placement and reduced spam classifications.
ISPs recognize and trust the sending domain.
How domain warming works in practice
The domain warming process is essentially a strategic ramp-up of your email volume. It begins with sending a small number of emails daily to a highly engaged audience, then slowly increasing that volume over several weeks or even months. This methodical approach mimics the organic growth of a legitimate sender, which ISPs are designed to favor.
Critical to this process is maintaining high engagement. ISPs pay close attention to metrics like open rates, click-through rates, and replies. Positive interactions signal that your emails are valued by recipients. Conversely, high bounce rates, spam complaints, or low engagement can quickly derail your warming efforts and trigger negative reputation scores. Therefore, selecting the right audience for initial sends and providing valuable content is paramount. Learn more about the email warm-up process for marketing senders from Microsoft Learn.
For new domains, establishing a strong foundation of positive sender reputation is particularly important, even for transactional emails. If you're using new domains on shared IPs, warming is still highly recommended. A typical warming schedule might look like this:
The double-edged sword of automated warming services
While the principle of domain warming is sound, the rise of automated warming services has introduced a contentious element. These services promise to automate the warming process by sending emails to a network of seed addresses, simulating opens and clicks. While this might appear convenient, it carries significant risks. Many ISPs are sophisticated enough to detect these artificial engagement patterns.
When an ISP identifies that you are using an automated warming service, it can lead to severe penalties. These include immediate blocklisting (or blacklisting) of your domain, reduced inbox placement, or even permanent damage to your sender reputation. The artificial nature of the engagement doesn't fool the sophisticated algorithms designed to detect genuine sender behavior. According to Postmark, if your mail is bad, all the warmup gimmicks in the world aren’t going to change that.
Although some users report short-term benefits from these services, these gains are often fleeting and unsustainable. The underlying issue of sending unwanted or low-quality emails remains unaddressed, meaning that once you transition to your actual campaigns, any artificially boosted reputation can quickly crumble. This is especially true for cold email, which can impact warm email deliverability and sender reputation.
The risks of artificial warming
Using automated warming services can lead to severe penalties from mailbox providers. These services often employ artificial engagement, which is easily detected by advanced spam filters.
Detection can result in your domain being blocklisted (or blacklisted), causing emails to be rejected or sent directly to spam. This can inflict long-term damage on your sending reputation, making it difficult to recover deliverability.
Focus on genuine engagement and organic list growth to build a sustainable and trusted sender reputation.
Building genuine domain reputation
For domain warming to be truly effective, it must be rooted in genuine engagement and a commitment to best practices. Instead of trying to trick ISPs, the focus should be on building a natural, positive relationship with them through consistent, wanted email sending. This approach yields sustainable deliverability benefits.
Key elements of effective, genuine domain warming include:
List hygiene: Start with a clean, opted-in list of engaged subscribers. Avoid old or purchased lists that may contain spam traps or unengaged users.
Content quality: Send valuable, relevant content that encourages opens, clicks, and replies. Engaged recipients are the best signals of a good sender.
Consistent sending: Maintain a steady sending volume once your domain is warmed. Avoid large, erratic spikes that can trigger spam filters. You can read more about how to improve email deliverability.
Reputation monitoring: Regularly check your domain's reputation using tools like Google Postmaster Tools to identify and address issues promptly.
Remember, the goal is to show ISPs that your domain is a source of wanted, legitimate email traffic. This genuine approach leads to lasting improvements in email deliverability and ensures your messages consistently reach the inbox, unlike the temporary and risky boosts offered by artificial warming methods.
The verdict on domain warming
Domain warming is undoubtedly effective for boosting email deliverability, but its success hinges on the approach. It's not a shortcut to bypass good sending practices; rather, it's a foundational process to establish and maintain a healthy sender reputation. For new domains or those undergoing significant changes, a structured, gradual warm-up is essential.
Relying on artificial warming services, while tempting, ultimately undermines your long-term deliverability goals. ISPs are increasingly adept at detecting and penalizing such tactics. True deliverability success comes from a commitment to sending desired content to an engaged audience, complemented by robust authentication and diligent monitoring. This genuine strategy ensures your emails consistently reach their intended recipients.
Views from the trenches
Best practices
Warm up organically by sending to highly engaged, opted-in recipients to build a strong sender reputation.
Isolate cold outreach and sales prospecting to separate domains and email accounts to protect your primary domain's reputation.
Focus on delivering genuinely good and desired content to your audience; this is the most effective form of warming.
Common pitfalls
Relying on automated warming services, which can lead to detection by ISPs and severe penalties like blocklisting.
Expecting short-term gains from artificial warming to translate into long-term deliverability success.
Sending unwanted or low-quality email content after a warm-up period, which quickly negates any reputation built.
Expert tips
Understand that mailbox providers can easily detect artificial warming patterns, often through subject line analysis or known seed addresses.
Prioritize real engagement metrics, such as opens, clicks, and replies, as these are critical for establishing and maintaining a positive sender reputation.
Remember that automated warming services are often used by senders who struggle to maintain a good reputation organically, seeing them as a workaround rather than a sustainable solution.
Marketer view
Marketer from Email Geeks says that automated warming services can lead to severe penalties if detected by abuse desks, resulting in account punishment.
2022-02-21 - Email Geeks
Marketer view
Marketer from Email Geeks says some email hosting providers automatically block emails from known mail warming seed addresses at the SMTP level.
Google and 
Microsoft, assess your domain's sending history and engagement metrics to determine where your emails should land. A new domain starts with a neutral reputation, which means it has no established history of good or bad sending practices. This lack of history often triggers stricter scrutiny, leading to higher chances of emails being marked as spam or blocked.
