What is the best approach for warming up an IP address for email sending?
Michael Ko
Co-founder & CEO, Suped
Published 23 May 2025
Updated 16 Aug 2025
8 min read
When you're preparing to send emails from a new IP address, whether you're migrating to a new email service provider (ESP) or expanding your sending infrastructure, you'll encounter the critical process of IP warming. Think of it like introducing yourself in a new community. You wouldn't immediately walk in and start shouting your opinions, would you? You'd start by being polite, engaging positively, and gradually building trust.
The goal of warming up an IP address is to establish a positive sender reputation with internet service providers (ISPs) and mailbox providers (MBPs). These providers, such as Gmail and Outlook, are wary of new IPs that suddenly start sending high volumes of email. Without a history, they can't distinguish between a legitimate sender and a spammer, so they often throttle or block new IPs by default. This is why a proper IP warming strategy is non-negotiable for anyone serious about email deliverability.
If you try to send your full volume right away, your emails are highly likely to land in spam folders, get rejected, or even cause your IP to be placed on an email blocklist (or blacklist), severely impacting your future sending success. An in-depth guide to email blocklists shows how crucial it is to avoid this fate.
The best approach involves a gradual increase in email volume, targeting your most engaged subscribers first, and closely monitoring your sending reputation. This deliberate, phased rollout demonstrates to ISPs that you are a legitimate sender sending desired content, helping your emails reach the inbox consistently.
The fundamentals of IP warming
IP warming is essentially a process of building trust. When an ISP sees email traffic from a new IP address, they have no historical data to evaluate its legitimacy. They rely heavily on initial sending patterns and recipient engagement to form a judgment. If you suddenly send hundreds of thousands of emails, it raises a major red flag, triggering their spam filters. ISPs use sophisticated algorithms that look at factors like sending volume, frequency, bounce rates, spam complaint rates, and engagement metrics (opens, clicks) to determine sender reputation. A high complaint rate, even from a small initial send, can severely damage your standing.
Therefore, the fundamental principle is to start small and incrementally increase your sending volume. This gradual ramp-up allows ISPs to observe positive sending behavior and consistently good engagement from your recipients. As your reputation grows, ISPs will become more accepting of larger volumes from your IP. This methodical approach minimizes the risk of your emails being flagged as spam or outright blocked, ensuring better email deliverability.
The length of the warming period can vary, typically ranging from a few weeks to several months, depending on your target volume and the responsiveness of your list. It's a dynamic process that requires careful observation and adjustments based on performance. The key is consistency and quality over speed. You're building a long-term relationship, not a quick transaction.
Crafting your IP warm-up schedule and content
The cornerstone of a successful IP warming strategy is your audience segmentation. You should always begin by sending to your most engaged subscribers. These are the people who consistently open, click, and interact with your emails. Their positive engagement sends strong signals to ISPs that your content is valued and desired. Starting with a highly engaged segment helps you quickly build a positive reputation.
Next, consider the type of content you're sending during the warmup phase. Transactional emails, like order confirmations, password resets, or shipping notifications, often have higher engagement rates because they are expected and essential. If possible, prioritize these for initial sends. For marketing emails, ensure your content is highly relevant, personalized, and provides clear value. Avoid promotional-heavy emails or anything that could trigger spam complaints during this sensitive period.
General IP warming schedule
This general schedule suggests volume increases over several weeks, but always adapt it based on your performance metrics. If you see high bounce rates or complaints, slow down.
Week 1: Start with 500 - 5,000 emails per day. Focus on your most active subscribers. Daily increases of 10-20% are typical.
Week 2: Gradually increase to 10,000 - 25,000 emails per day. Continue adding highly engaged recipients, broadening your segment slightly.
Week 4+: Continue doubling volume as long as metrics remain positive, incorporating more of your list. The warm-up process for marketing senders often extends for several more weeks to reach full volume.
Maintaining a consistent sending frequency is also vital. If you plan to send daily after warming, you should try to send daily during the warm-up, albeit at lower volumes. This helps ISPs understand your typical sending patterns, ensuring they don't get 'surprised' by a sudden change in frequency once warming is complete.
Monitoring, authentication, and list hygiene
Monitoring your email performance during IP warming is paramount. Pay close attention to your bounce rates (soft and hard bounces), spam complaint rates, open rates, and click-through rates. These metrics provide direct feedback on how ISPs and recipients are responding to your new IP. Tools like Google Postmaster Tools and other similar services are indispensable for gaining insights into your sender reputation and deliverability issues.
Ensuring your email authentication protocols are correctly configured is another critical best practice. SPF, DKIM, and DMARC records prove that your emails are legitimate and prevent spoofing. Properly implemented authentication adds another layer of trust with ISPs, which is especially important during the warming phase.
Finally, maintaining a clean and engaged email list is fundamental to successful IP warming and long-term deliverability. Regularly remove inactive subscribers, hard bounces, and any addresses that have marked your emails as spam. Sending to spam traps can instantly land your IP on a blocklist (or blacklist), negating all your warming efforts. A healthy list ensures that the engagement signals you send to ISPs are overwhelmingly positive.
Advanced tactics for a smoother warm-up
Beyond the core principles, there are advanced techniques that can smooth out your IP warming process. One effective method is to throttle your sends throughout the day, rather than sending everything in one large burst. This mimics natural sending behavior and can help avoid temporary throttling by ISPs. For instance, instead of sending 50,000 emails at 9 AM, you might spread them out at 5,000 emails per hour over 10 hours. Additionally, prioritize sending to your most engaged recipients during the first hours of the day to maximize initial positive signals.
Be aware of ISP-specific nuances. While general warming principles apply, some providers have particular sensitivities. For example, some mail providers, like Yahoo, are known for strict throttling if they detect rapid volume increases or poor engagement. Specific error codes, like TSS04 from Yahoo, can indicate you're warming up too quickly. Adapting your schedule to these signals is key for successful deliverability, particularly for large senders. You can learn more about IP warming strategies by ISP.
For very large sending volumes or complex email programs, investing in a Customer Data Platform (CDP) or advanced marketing automation platform can provide the granular control needed for sophisticated warming. These platforms often offer flexible workflows, segmentation capabilities, and throttling options that allow you to precisely control who receives emails, when, and at what volume. This level of control can make the difference between a smooth warm-up and frustrating deliverability challenges.
Views from the trenches
Best practices
Start with the most engaged segment of your audience, as their positive interactions will build trust quickly with ISPs.
Maintain a consistent sending schedule during the warm-up that mirrors your intended long-term frequency.
Use email content that recipients expect and find valuable, such as transactional or highly personalized messages, to maximize engagement.
Continuously monitor key metrics like open rates, click-through rates, and bounce rates to gauge your IP's reputation.
Implement email authentication protocols (SPF, DKIM, DMARC) before starting the warm-up to ensure email legitimacy.
Gradually increase your sending volume, starting small and doubling only when performance metrics remain strong.
Common pitfalls
Sending full email volume immediately from a new IP, leading to instant throttling or blacklisting.
Ignoring engagement metrics during warm-up, missing crucial signals of poor performance.
Sending to unengaged or old lists, which can trigger spam traps and damage sender reputation.
Inconsistent sending patterns, such as sporadic sends or sudden large volume spikes.
Using low-quality or overly promotional content during initial warm-up phases, increasing complaint rates.
Not cleaning your email list before warming up, risking high bounce rates and spam reports.
Expert tips
Segment your list by engagement level for precise control over warm-up sends.
Spread out your daily sends throughout the day to avoid throttling and mimic natural traffic.
Pay close attention to ISP-specific feedback, like Yahoo's TSS04 errors, and adjust your sending.
Use a Customer Data Platform (CDP) for advanced segmentation and throttling capabilities.
Don't resend identical emails to the same recipient during the warm-up period.
Remember that email deliverability is an ongoing process, not just a one-time warm-up event.
Expert view
Expert from Email Geeks says to send during warm-up as you would after warm-up, as you are setting expectations.
2021-11-17 - Email Geeks
Expert view
Expert from Email Geeks says recipients would not be pleased if they received identical emails repeatedly, so have new content ready.
2021-11-17 - Email Geeks
The path to reliable deliverability
Warming up an IP address for email sending is a foundational step for ensuring robust deliverability and a strong sender reputation. It's a strategic investment of time and effort that pays dividends in long-term inbox placement and campaign success. By adhering to a methodical schedule, focusing on high-engagement segments, diligently monitoring your performance, and maintaining impeccable list hygiene, you can successfully establish trust with ISPs. This approach not only prevents your emails from landing in the spam folder, but also sets the stage for a reliable and effective email program.
Gmail and 
Outlook, are wary of new IPs that suddenly start sending high volumes of email. Without a history, they can't distinguish between a legitimate sender and a spammer, so they often throttle or block new IPs by default. This is why a proper IP warming strategy is non-negotiable for anyone serious about email deliverability.
