IP warming: How to build a trusted sender reputation and improve email deliverability

How to warm up an IP

1. Start with small email sends
2. Ramp volume gradually
3. Target engaged subscribers
4. Monitor engagement (and adjust accordingly)

What is IP warming?

Email remains one of the most powerful marketing channels—but only if messages actually reach the inbox. After all, even the most creative campaigns can underperform if mailbox providers flag them as suspicious. That’s why email deliverability, and the practices that protect it, are critical for email marketing’s long-term success.

IP warming is the gradual ramp-up of email volume on a new IP address to build a trusted sender reputation with mailbox providers. Done correctly, this process can improve deliverability, protect inbox placement, and help avoid spam filters.

By understanding how IP warming works, why it matters, and the best practices involved, marketers can protect sender reputation from day one and set their email programs up for scalable, sustainable growth.

Why IP warming Is critical

When it comes to email marketing, there’s no bigger make-or-break factor than email deliverability. You can craft beautiful designs, write compelling copy, and build irresistible offers…but if your emails don’t make it into the inbox, none of that matters. That’s why IP warming is the first step in building a strong foundation for successful, consistent inbox placement.

Protecting inbox placement

Mailbox providers use complex algorithms to decide whether a message lands in the inbox, the promotions tab, or the spam folder. Brand-new IP addresses and subdomains without sending histories are treated with caution. Without proper warming, your carefully built campaign could be throttled (sent more slowly than intended), filtered by spam filters, or even outright rejected. By following a measured ramp-up schedule, you have an opportunity to prove to providers that your sends are legitimate, engaging, and trustworthy – and that you're sending what your subscribers expect and want to receive.

Building a strong sender reputation

Your IP and subdomain reputations are a direct reflection of how mailbox providers view your email program. Positive signals—like strong open rates, consistent volume, and low spam complaints—improve reputation and long-term inbox placement. Negative signals, like high bounce rates or sudden spikes in volume, can damage credibility and trigger filters. Once reputation is harmed, recovery is slow and difficult. Trust-building through IP warming helps you start off on the right foot.

The cost of skipping IP warming

Skipping IP warm up can be expensive. If providers blocklist your IP, your reach will drop, resource costs may increase and revenue may suffer. IP warming is essential for every sender, regardless of industry. Micro IP warming (that is, warming smaller audiences to support specific planned sends or campaigns) may even be necessary when sending volume is expected to increase significantly, such as with seasonal spikes or after a business acquisition. Picture a retailer launching a holiday push from a cold or low volume IP: Open rates can be dramatically cut as spam filters step in, wiping out seasonal sales and damaging IP reputation. The harm goes beyond open rates. It also undermines customer experience when onboarding messages, order updates, or offers never arrive. IP warming protects inbox placement so emails are seen, opened, and acted on.

How to warm up an IP (step-by-step)

Successful IP warming comes from consistency, trust-building, and close attention to detail. Rushing the process almost always undermines deliverability. Here’s a clear roadmap to follow:

1. Create a ramp-up schedule

Start with a small, manageable number of emails on day one; think 50-100 per sending IP, rather than your full list. Gradually increase your volume each day or week, depending on your overall sending goals. This throttling approach lets mailbox providers see steady, predictable growth, rather than sudden, suspicious spikes.

Example ramp-up:

• Day 1: 50
• Day 2: 100
• Day 3: 500
• Day 4: 1,000
• Day 5: 5,000
• Day 6: 10,000
• Day 7: 20,000
• Day 8: 40,000
• Day 9: 70,000
• Day 10: 100,000
• Day 11: 150,000
• Day 12: 250,000
• Day 13: 400,000
• Day 14: 600,000
• Day 15: 1,000,000
• Day 16: 2,000,000
• Day 17: 4,000,000
• Day 18+: Continue scaling until full program volume

Remember, the ideal pace depends on your audience size, your list health, the receptivity of the audience you are targeting and how many emails you ultimately plan to send regularly. In practice, IP warming usually takes between two and six weeks, depending on your total audience size, sending frequency, and engagement levels. Smaller senders may finish more quickly, while high-volume programs often need the full timeline to build a stable reputation. Plus, different mailbox providers may respond at different speeds. Gmail, Outlook, and Yahoo each have their own filters, so keep an eye on performance indicators, such as open rates, complaint rates and reputation reporting (if available) when scaling.

2. Start with responsive subscribers

Begin with your most engaged segments—the people who reliably open and click. Good groups to start with may look like:

• Recent activity cohorts (opened/clicked in the last 30–90 days)
• Double opt-in or confirmed subscribers
• VIP/loyalty or frequent purchasers

These audiences generate positive signals (high opens/CTR, low complaints) that strengthen sender reputation. Hold back inactive or unverified addresses until the IP shows stable performance (and take a methodical, careful approach when you do incorporate less-engaged subscribers).

3. Monitor key engagement metrics

Keep a close eye on deliverability signals throughout the process, including:

• Open rates: Measure interest and inbox placement success
• Click-through rates (CTR): Show real engagement
• Bounce rates: Flag data quality issues
• Spam complaints: The most damaging signal for IP reputation

These metrics act as feedback loops from mailbox providers. Use them to fine-tune your pace and avoid deliverability setbacks.

4. Adjust cadence based on feedback

Let the data set the pace. If metrics are solid, keep increasing volume on schedule. If you see rising complaints, elevated bounces, or provider-specific deferrals consider:

• Holding at current volume or rolling back one step until metrics recover
• Pausing new cohorts; send only to your most responsive segments
• Triaging by provider (e.g., slow Outlook sends if only Outlook is spiking)
• Addressing root causes (list hygiene, customer reception, template issues, broken links, frequency)

Small, timely adjustments prevent minor issues from becoming deliverability setbacks and keep your warm-up on track.

Common mistakes to avoid

Even experienced marketers can stumble when it comes to IP warming. Avoiding these pitfalls will save you time, protect your sender reputation, and ensure stronger long-term inbox placement.

1. Sending to unengaged or purchased lists

Starting your warm-up with disengaged subscribers, users with misspelled email addresses (or worse, purchased lists, which is against the Braze Acceptable Use Policy) is a fast track to trouble. Low engagement and high spam complaints signal to mailbox providers that your emails aren’t wanted. That can lead to throttling, spam folder placement, or outright blocking. Always begin with your most active, opted-in audience and add less-engaged contacts in a systemized, cautious method only after your IP shows healthy performance.

2. Scaling volume too quickly

It can be tempting to speed through the IP warm up process, especially when you have deadlines or seasonal campaigns on the horizon. But sending too many emails too soon can trigger spam filters. If mailbox providers see unnatural spikes in volume from a new IP, they may route your messages to the junk folder or block them entirely. Rushing the process can actually extend the overall length of the warming period due to problems that may arise.

3. Ignoring engagement signals

Engagement metrics like open rates, click-through rates, bounce rates, and spam complaints are more than vanity numbers—they’re vital signals of your IP reputation. If you ignore these red flags and keep increasing volume in the face of worrying results, you risk permanent damage to your standing with mailbox providers. Treat these signals as guardrails. If complaints rise or engagement drops, slow the ramp and fix the root cause.

IP warming best practices

At its core, IP warming is less about the mechanics of volume increases and more about building enduring trust with mailbox providers to ensure strong deliverability. Following these email warm-up best practices will help you establish a strong sender reputation and keep your messages in the inbox where they belong.

1. Authenticate your domain

Before sending a single message, make sure your domain is fully authenticated with the Sender Policy Framework (SPF), Domain Keys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting, and Conformance (DMARC) protocols. These protocols prove your legitimacy, reduce the risk of spoofing, and are often required by mailbox providers for optimal inbox placement. Without this step, even a perfect ramp-up schedule may struggle to achieve strong inbox placement. Think of authentication as your passport. It reinforces to providers you are who you claim to be.

2. Start with engaged audiences

Your first sends should go to your most engaged subscribers. Their positive engagement reinforces to mailbox providers that your messages are valued, setting the stage for broader sending later. Starting here not only improves inbox placement but also protects your long-term IP reputation.

3. Maintain consistency in volume and frequency

Mailbox providers look for predictability. Sending in erratic bursts or dropping off suddenly can raise red flags. Stick to a steady ramp-up schedule, keep frequency consistent, and aim for a sustainable sending pattern beyond the warm-up period. For high-volume senders, even small fluctuations can signal instability to mailbox providers.

4. Monitor and adjust based on data

No two warming schedules are exactly alike. Monitor engagement metrics like open rates, click-through rates, bounce rates, and spam complaints. If engagement dips or complaints rise, pause your ramp-up and troubleshoot before moving forward. Staying responsive to mailbox provider feedback shows that you’re prioritizing end user experience over volume.

How Braze simplifies IP warming

While IP warming is critical, it can also be complex and time-consuming if done manually. With Braze automated IP warming, marketers can rely on automated schedules and AI-assisted optimization, removing the manual guesswork.

Automated IP warming schedules

Braze simplifies the ramp-up process with automated schedules built directly into our product. Instead of juggling spreadsheets or guessing daily send volumes, teams can follow a structured plan that scales safely and efficiently. Automation also reduces the risk of human error, helping brands stick to a consistent cadence.

AI-assisted optimization

With BrazeAI™, marketers can take the guesswork out of warming. The platform recommends optimal send volumes and cadence based on previous engagement metrics and mailbox provider feedback. This data-driven approach ensures you through your IP warm up at the right pace, while also allowing for adjustments when signals shift.

Real-time reporting dashboards

Braze provides real-time analytics to track delivery bounce rates, spam complaints, and other key deliverability signals during the warm-up phase. Having this visibility in one place helps teams identify potential issues early and make informed adjustments before they escalate. For larger teams, these dashboards also serve as a single source of truth across marketing and deliverability stakeholders.

Expert deliverability services

For brands that want extra support, Braze offers access to a dedicated Email Deliverability Services team. These experts provide hands-on guidance, helping you design custom ramp-up schedules, monitor, troubleshoot and navigate issues, and protect your long-term IP reputation. Expert services are particularly valuable for senders that lack deliverability expertise, manage complex email programs, and/or don’t have dedicated monitoring and incident response in place.

Final thoughts: Building email programs that last

IP warming lays the groundwork for the long-term health and scalability of your email program. By starting with trust-building practices and staying attentive to mailbox provider signals, brands ensure that every campaign has the best chance to reach and resonate with customers.

With Braze, teams can approach the IP warming process with confidence. Automated schedules, BrazeAI™ optimization, and real-time reporting streamline the path to a trusted IP reputation, while expert deliverability guidance provides intensive support, both initially and ongoing. The result is an email strategy that not only makes it to the inbox but also drives sustainable growth and stronger customer relationships over time.