Modern email service providers recognize and filter out spam messages. Emails from unfamiliar IP addresses, especially many at once, send up red flags that trigger the filter. Unfortunately, an overzealous filter might wrongly flag your legitimate marketing emails. How can you ensure your messages reach the intended recipient?

For new systems, IP warming is one of the most critical steps in ensuring your emails land in inboxes—not spam folders. This strategic process gradually builds the credibility of your IP address, paving the way for successful email delivery. Here’s everything you need to know about IP warming and how to execute it effectively.

Action Required: Prepare for Outlook’s New Rules

Big news for email senders! Outlook is dropping stricter authentication rules (SPF, DKIM, DMARC) after May 5th, 2025, especially for high-volume senders. No authentication = straight to junk! This makes warming up your IP and building trust absolutely ESSENTIAL right now. Don’t get left behind!

What Is IP Warming?

IP warming is the gradual process of increasing the volume of emails sent from a new or dormant IP address. The goal is to establish a positive sender reputation with internet service providers like Gmail, Yahoo, and Hotmail. Without proper warming, ISPs may flag your emails as spam due to an unproven reputation.

Why is this so crucial? ISPs and email filters rely on sender behavior and engagement metrics to determine email deliverability. A sudden surge in email volume from an unfamiliar IP address could trigger alarms, leading to deliverability issues. Proper IP warming prevents this by demonstrating consistent, high-quality sending behavior over time.

Major email providers like Outlook are increasingly getting strict about email authentication. Starting May 2025, high-volume senders must have SPF, DKIM, and DMARC properly configured to avoid the junk folder. Considering that a significant portion of cold email senders neglect these crucial steps, the importance of building a positive sender reputation through IP warming becomes even clearer for new IP addresses.

How to Warm Up Your IP Address

Start Slow

Begin with small, controlled batches of emails sent to your most engaged recipients. Focus on new subscribers and those who have opened or clicked on one of your marketing emails within the last six months. Avoid sending to older or less active addresses, as these are more likely to trigger spam complaints or hit spam traps.

Are you wondering which subscribers to target first? Your best bet is recent purchasers, frequent website visitors, and those who’ve explicitly opted in within the last 30 days. These folks are practically waiting to hear from you!

Focus on High-Quality Content

In this early stage, the more engaging content you share, the higher your chances of getting clickthrough. Use campaigns designed to increase recipient interest, such as:

• Welcome emails for new subscribers.
• Awareness campaigns promoting your new sender identity (e.g., encouraging recipients to add your email to their address books).
• Proven content that has performed well in past campaigns.

Follow a Gradual Volume Increase

Use a phased approach to increase daily email volumes across your subscriber base. As your reputation improves, you can expand your reach to re-engage older contacts. For example:

• On day one, send 200 emails to Gmail and 500 to smaller ISPs.
• By day seven, gradually ramp up to 7,000 emails to Gmail and 14,000 emails overall.
• The key is maintaining steady volumes for a few days at each stage before scaling up further.

IP Warming Calendar Template

You may follow the below given IP warming calendar template for your IP warming strategy. Based on list size of your subscribers & clients the numbers can be varied proportionally.

Day	Gmail Recipients	Yahoo/Outlook Recipients	Other ISPs	Total Daily Volume
1-2	200	200	500	900
3-4	500	500	1,000	2,000
5-7	1,000	1,000	2,000	4,000
8-10	2,500	2,500	4,000	9,000
11-14	5,000	5,000	7,000	17,000
15-21	7,500	7,500	10,000	25,000
22-30	10,000+	10,000+	15,000+	35,000+

Monitor and Adjust

Track metrics such as bounce rates, open rates, and spam complaints regularly. If performance declines, slow down the warming process or refine your recipient list to exclude problematic addresses. Seeing those bounce rates creep up? That might be a sign to slow down your volume increases. Remember, it’s better to take an extra week warming up than to rush and damage your sender’s reputation.

Advanced Ramp-Up Strategies

After successfully completing the warming phase, you can move into the ramp-up phase to reach your full sending capacity. This phase involves incremental increases in volume over several weeks. Depending on your level of aggressiveness, volume can be increased by 25% to 50% every 2-3 days. However, proceed with caution—poor-quality data or overly aggressive ramp-ups can harm your IP reputation.

Common IP Warming Pitfalls to Avoid

• Going Too Fast

The most common mistake we see is rushing the process. Even if your marketing calendar is packed, stick to the plan. Those emails won’t help if they never reach the inbox.

• Ignoring Warning Signs

If you notice a sudden drop in open rates or increase in spam complaints, don’t push forward. Take a step back, analyze what’s happening, and adjust your approach.

• Sending to Cold Subscribers

That list of 50,000 subscribers who haven’t engaged in 18 months? Save them for later—much later—in your warming process, if at all.

• Using Low-Quality Content

Your very best content should go out during warming. This isn’t the time to test that experimental campaign you’ve been unsure about.

Industry-Specific Warming Tips

• B2B marketers often require longer warming periods due to reduced engagement rates. Consider implementing a 6–8 week plan instead of a 4-week one.
• E-commerce – Focus initial sends on recent purchasers and cart abandoners—they have the highest engagement potential.
• Financial Services – Be extra cautious with volume increases, as many financial domains have stricter spam filtering policies.

Troubleshooting Guide:

What to Do If…

• Your Bounce Rate Exceeds 5%

Immediately halt volume increases and review your most recent subscriber additions. You must also check for sending domain issues and consider temporarily decreasing the volume.

• Your Emails Are Being Bulked (Sent to Spam)

Focus exclusively on your highest-engagement segments. Simplify email design and reduce the image count. Check your authentication records (SPF, DKIM, DMARC) and review your content for spam trigger words.

• Engagement Suddenly Drops

Verify your sending domain isn’t on any blacklists. Then check for recent content for any potential rendering issues across devices. You may try to reduce your sending volume temporarily while you fix the issues before resuming your IP warming. Switching to your highest performing email template may also aid in overcoming the issues.

Key Takeaways for Successful IP Warming

• Engagement is king: Target only highly engaged recipients to maximize positive feedback and minimize complaints.
• Slow and steady wins the race: Abrupt increases in volume are a surefire way to raise red flags with ISPs.
• Stay vigilant: Monitor your performance metrics and adjust your approach as needed.
• By following these best practices, you’ll establish a strong sender reputation and set your email marketing campaigns up for long-term success.

Final Words

Successfully reaching your audience’s inbox is crucial for any new marketing push or when transitioning to a new IP. However, without careful preparation, deliverability can be a significant hurdle. Taking the time to properly warm up your IP is therefore a vital investment. This foundational step ensures your emails are welcomed, ultimately leading to stronger engagement and the success of your email campaigns.