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IP Warming: Gradual Sending Explained

September 2, 2025

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5 min read

IP warming is the process of slowly increasing the number of emails sent from a new or dormant IP address to build trust with Internet Service Providers (ISPs). This ensures emails land in inboxes, not spam folders. Here's the key takeaway:

Skipping IP warming can harm your sender reputation, leading to blocklisting or poor deliverability. Tools like Mailforge simplify the process by automating technical setups, managing domains, and scaling infrastructure to ensure smooth email outreach. Proper IP warming is critical for successful email campaigns.

Why Gradual Sending Improves Deliverability

Gradual sending plays a crucial role in safeguarding your sender reputation, especially when paired with IP warming. By increasing email volume step by step, you reduce risks and establish trust with Internet Service Providers (ISPs), who constantly monitor your reputation to shield users from spam and harmful content.

How ISPs Check Sender Reputation

Big-name ISPs like Gmail, Outlook, and Yahoo use sophisticated algorithms to evaluate sender reputation. They focus on several factors, including engagement signals. Positive interactions - like opening emails or clicking links - boost your reputation. On the flip side, actions like deleting emails without opening, marking them as spam, or ignoring them altogether can hurt your standing.

Bounce rates are another key metric ISPs monitor. Hard bounces, caused by invalid email addresses, and soft bounces, linked to temporary delivery issues, both impact how reliable you appear as a sender. Keeping bounce rates low is essential.

ISPs also look at your sending patterns. Abrupt increases in email volume, irregular sending schedules, or targeting mostly inactive recipients can raise suspicion. They compare your activity to historical trends and industry norms to catch anything out of the ordinary. Proper email authentication - using SPF, DKIM, and DMARC records - is another way to prove legitimacy. Without these measures, large-scale email campaigns can easily trigger ISP scrutiny.

Problems with High-Volume Sending Without Warming

Jumping straight into high-volume email campaigns from a new IP can lead to serious problems. ISPs are likely to flag a sudden spike in email traffic as spammy behavior, which can result in emails being filtered into spam folders or throttled. Throttling, or rate limiting, means only a fraction of your emails will actually reach their destination.

An even bigger concern is blocklisting. If your sending practices seem suspicious, your IP could end up on an ISP's blocklist, severely impacting your ability to deliver emails across multiple platforms. Repairing a tarnished reputation after being blocklisted can be a long and challenging process.

How to Send Gradually

The key to successful IP warming and improved deliverability is a gradual approach. Start by sending a small number of emails to your most engaged contacts, then slowly increase the volume over several weeks. This allows ISPs to observe consistent, positive engagement before you scale up further.

Recipient selection is critical during this process. Focus on active contacts - those who’ve recently interacted with your emails - and remove or segment inactive ones. Cleaning your email list beforehand to eliminate invalid addresses is another important step to avoid unnecessary bounces.

During the warming phase, prioritize quality content. Instead of sending purely promotional messages, provide useful, relevant information that encourages engagement. Timing also matters - send emails during peak business hours on weekdays when recipients are most likely to engage.

Track engagement daily. If you notice a dip in open or click rates, adjust your sending volume accordingly. You might also want to start with recipients in the same region as your IP, gradually expanding to international audiences. This creates a natural, consistent sending pattern that ISPs are more likely to trust.

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IP Warming Process Step by Step

To implement IP warming effectively, you need to gradually increase your email volume while keeping a close eye on key engagement metrics. Here’s a detailed guide to help you build a strong sender reputation and ensure successful email outreach.

Starting Volume and How to Increase

Start small - send 50-100 emails per day during the first week. This cautious beginning allows Internet Service Providers (ISPs) to observe your sending activity without raising any red flags or triggering spam filters. Keep your daily volume consistent during this phase. Avoid abrupt spikes or irregular sending patterns, as these can harm your reputation.

In the second week, double your daily volume to 100-200 emails. Continue this pattern of doubling each week until you’re sending 1,000–2,000 emails daily within 4–6 weeks. The goal is steady, gradual growth - not rapid increases. If you notice a rise in bounce rates or spam complaints, pause the volume increase and maintain the current level for another week to stabilize your metrics.

It’s also wise to avoid sending emails on weekends during the warming phase. Engagement rates tend to drop over weekends, which can negatively impact the reputation you’re trying to build. Once your sending schedule is established, focus on targeting your most engaged contacts to maximize positive interactions.

Choosing the Right Recipients

Start with the people who are most likely to engage - your most active contacts. These are the recipients who have opened or clicked your emails within the past 30 days. Their positive interactions send strong signals to ISPs, helping to build your sender reputation more effectively.

Use a tiered approach for selecting recipients. In the first two weeks, send emails exclusively to your most recent and active contacts. Avoid using purchased lists or reaching out to cold contacts during this phase. These recipients are less likely to engage and more likely to generate bounces or spam complaints, which can derail your progress.

Geographic targeting is another important consideration. If your IP address is based in the United States, begin by sending emails to US-based recipients. ISPs like Gmail, Outlook, and Yahoo often evaluate domestic traffic differently from international sends. Building a strong reputation locally can create a solid foundation for expanding globally.

Finally, clean your email list before starting. Remove any addresses that have bounced in previous campaigns. A clean list is critical - bounce rates above 5% can signal poor list hygiene to ISPs and slow down your reputation-building efforts.

Tracking Performance Metrics

Once you’ve defined your volume and recipient strategy, tracking performance metrics becomes crucial. Monitor key indicators like open rates, click rates, and bounce rates to ensure your campaign is on track. Aim for:

If your bounce rate exceeds 2%, it’s a sign of list quality issues that need immediate attention. Separate hard bounces (permanent issues) from soft bounces (temporary issues). Hard bounces should be removed from your list right away, while soft bounces might resolve over time.

Spam complaints are another critical metric. Keep your complaint rate below 0.1% (1 complaint per 1,000 emails). Even a small increase in complaints can lead to ISP filtering or throttling. Many email service providers offer feedback loops to alert you to complaints, so you can quickly remove those recipients from future sends.

Additionally, track delivery rates and inbox placement to understand how ISPs perceive your sender reputation. Tools that monitor deliverability can show whether your emails land in the inbox, spam folder, or are blocked entirely. Consistent inbox placement above 85% is a good sign that your reputation is improving.

Pay attention to engagement timing as well. Quick opens and clicks indicate a strong sender reputation, while delayed engagement might suggest initial filtering issues that should resolve as your reputation grows.

Keep a detailed weekly log of your sending volumes, engagement rates, and deliverability metrics. This data will help you spot trends and make informed decisions about when to increase volume or adjust your strategy. Remember, successful IP warming typically takes 6–8 weeks, so patience and consistent monitoring are key to long-term success.

How IP Warming Affects Email Campaign Results

Taking the time to properly warm up your IP can significantly improve your sender reputation, leading to better performance for your email campaigns. Let's dive into how this process impacts inbox placement and overall engagement.

Better Inbox Placement and Engagement

When done right, gradual IP warming can lead to inbox placement rates as high as 96–98%. This means your emails are more likely to land in the primary inbox rather than being shuffled into spam or promotions folders. And when your messages consistently reach the right inbox, you'll see a natural boost in open rates, click-through rates, and overall engagement.

During the warming process, major email providers like Gmail, Outlook, and Yahoo begin to recognize your sending patterns as legitimate. This trust reduces the likelihood of your emails being flagged as spam and minimizes filtering issues. A strong sender reputation not only allows you to scale up your email volume without triggering alarms but also provides a buffer against occasional dips in quality or seasonal fluctuations. Essentially, a good reputation ensures that your campaigns maintain consistent deliverability, even when reaching out to less engaged lists.

Problems from Skipping or Poor Warming

Jumping straight into high-volume email sending without properly warming up your IP can backfire in a big way. Internet Service Providers (ISPs) may see this behavior as suspicious, leading to blacklisting or having your emails automatically diverted to spam or bulk folders.

The consequences of skipping or mishandling the warming process go beyond marketing emails. Even transactional messages and customer service communications can be affected if your IP gains a bad reputation. These issues highlight why a gradual, methodical approach to IP warming is essential.

Benefits of Gradual Warming

Taking the gradual route when warming your IP comes with clear advantages, especially when compared to rushing into high-volume sending. Here's how the two approaches stack up:

Gradual IP Warming
Rushed High-Volume Sending

96–98% inbox placement rates
Lower inbox placement rates

Smooth scalability
Risk of volume restrictions and reputation harm

Builds trust with email providers
Increased risk of blacklisting

Consistent performance over time
Deliverability issues over the long term

Protection against reputation dips
Vulnerable to sudden problems

Early detection of issues
Problems only identified after damage occurs

Lower marketing waste
Higher costs per successful delivery

Improved engagement metrics
Poor open and click rates

By gradually increasing your sending volume, you're able to identify potential issues - like a rise in bounce rates or a drop in engagement - before they spiral into bigger problems. This proactive approach not only safeguards your sender reputation but also ensures your campaigns continue to run smoothly.

Additionally, a measured warming strategy helps protect your entire email ecosystem. Whether it's customer communications, automated workflows, or marketing campaigns, a steady approach keeps everything functioning reliably as you scale your outreach efforts.

How Mailforge Supports Scalable IP Warming

Managing IP warming manually can be overwhelming, especially when scaling cold email outreach. Mailforge simplifies this process by offering a shared cold email infrastructure that takes care of the technical complexities, letting you focus on creating impactful campaigns. Here’s how Mailforge’s features make scalable and efficient IP warming possible.

Mailforge Features for IP Warming

Mailforge streamlines the setup of SPF, DKIM, and DMARC protocols, saving you hours of manual work. With these authentication measures in place from day one, your domains are set up for success, ensuring a solid foundation for IP warming. This aligns perfectly with the gradual sending strategy needed to build a positive reputation.

The platform also excels in bulk domain management, making it easy to handle hundreds or even thousands of domains. Instead of spending days on manual setups, you can configure multiple domains in just minutes.

For added professionalism and security, Mailforge offers SSL and domain masking at $2 per domain per month (or $6 annually). This feature boosts trustworthiness, which is critical during the early stages of warming. Trust signals like these can make a big difference to both ISPs and recipients.

One standout feature is Mailforge’s compatibility with any sending software. Whether you’re using popular email tools or custom-built solutions, you can integrate Mailforge seamlessly without needing to overhaul your existing workflows. This flexibility allows you to start warming IPs immediately without disruptions.

Scaling Outreach with Mailforge

Mailforge’s ability to create and manage hundreds or thousands of domains and mailboxes in minutes is a game-changer for scaling operations. This speed is crucial because distributing your sending volume across a properly configured infrastructure helps you build reputation faster. It also supports the gradual volume increase necessary for successful IP warming.

Mailforge’s pricing is designed to scale with your needs, making enterprise-level infrastructure accessible to businesses of all sizes. The platform includes a cost calculator to help you budget accurately for your specific requirements, ensuring predictable expenses as you increase sending volumes.

For agencies managing multiple campaigns, Mailforge offers separate workspaces. This ensures that each campaign maintains its own sender reputation, preventing issues with one campaign from affecting others. This isolation is especially valuable when handling multiple clients.

Integration with Other Forge Products

Mailforge’s infrastructure becomes even more powerful when integrated with other Forge tools. For example, Warmforge, a dedicated email deliverability platform, automates warm-up sequences and placement tests, ensuring your Mailforge setup is optimized for deliverability from the start.

For businesses needing private infrastructure, Infraforge provides dedicated IP warming with multi-IP provisioning and API access. This allows you to begin with Mailforge’s shared infrastructure and smoothly transition to private infrastructure as your volume grows.

Additionally, Salesforge integrates directly with Mailforge, enabling you to run warming campaigns and scale into full outreach without switching platforms. This seamless transition ensures that the sender reputation you’ve worked hard to build carries over into your active campaigns.

Together, these tools create a unified system where IP warming is not a separate, complicated task - it’s a built-in feature of your email infrastructure, designed to grow with your business needs.

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Conclusion

Throughout this guide, we've seen how IP warming plays a critical role in ensuring email outreach success. It's not just about meeting technical requirements - it’s about building the foundation for reliable email deliverability. Without proper IP warming, even the most well-crafted email campaigns can fall flat.

The process is straightforward: start with small sending volumes and gradually increase them over 4-6 weeks. This approach helps Internet Service Providers (ISPs) recognize your legitimacy, leading to better inbox placement, improved engagement, and stronger long-term deliverability.

That said, managing IP warming manually can quickly become overwhelming, especially as your email outreach scales. This is where Mailforge steps in. Mailforge simplifies the process by automating technical setups like domain configuration, DNS management, and infrastructure handling. With its ability to create and manage hundreds of domains in just minutes, you can focus on crafting impactful campaigns instead of getting bogged down in technical details.

Mailforge is designed to work seamlessly with any sending software, so you don’t have to overhaul your existing workflows. Whether you’re an agency juggling multiple clients or a large enterprise scaling outreach efforts, Mailforge’s shared infrastructure ensures reliable email deliverability at scale.

When paired with other Forge products - like Warmforge for automated warm-up sequences and Salesforge for campaign execution - Mailforge takes your IP warming efforts to the next level. These tools create a smooth transition from warming up your IP to running active campaigns, all while maintaining the sender reputation you’ve worked hard to establish.

In short, successful cold email outreach begins with proper IP warming. By adopting a gradual approach and leveraging tools built for scalability, businesses can ensure consistent inbox placement and drive meaningful results. With streamlined processes in place, transitioning from IP warming to impactful campaigns becomes a seamless journey.

FAQs

Why is it essential to focus on engaged contacts during the IP warming process?

When you're working on IP warming, prioritizing engaged contacts is key. Why? Because it builds a strong sender reputation with email providers. When recipients consistently open, read, and interact with your emails, it signals to email systems that your messages are worth delivering.

This early activity boosts critical metrics like open and click rates, which play a huge role in ensuring your emails land in inboxes - not spam folders. By focusing on active, interested contacts from the start, you're setting yourself up for lasting success with email deliverability.

What should I do if my engagement metrics drop during IP warming?

If you notice a dip in your engagement metrics during the IP warming process, it’s time to take a closer look at key indicators like open rates, click-through rates, bounce rates, and spam complaints. A downward trend in these areas could mean it’s time to tweak your approach.

Start by temporarily reducing your email sending volume. Focus on targeting your most engaged recipients - those who are already interacting with your emails. This strategy helps protect your sender reputation while boosting deliverability. As you see engagement improve, slowly ramp up your sending volume. The key is to make gradual adjustments and keep a close eye on your metrics to ensure your IP warming process stays on track.

Why is email authentication important during IP warming, and how can I make sure my emails are properly authenticated?

Email authentication plays a key role in IP warming, as it helps establish trust with Internet Service Providers (ISPs) and mailbox providers. This trust is essential for ensuring your emails land in recipients' inboxes. By using protocols like SPF, DKIM, and DMARC, you confirm that your emails are legitimate and not spam, which is crucial for maintaining a good sender reputation.

Here’s how these protocols work and why they matter:

Setting up these protocols correctly in your DNS records is non-negotiable. When properly configured, they not only support a smoother IP warming process but also help boost your email deliverability over time.