The Email Warm-Up Process: A Guide to Scaling
Email warm-up is an essential process for establishing and maintaining a positive reputation for your sending domain and IPs. Whether you’re transitioning to a new email service provider (ESP) or starting fresh, warming up your email infrastructure gradually helps ensure high deliverability, avoids spam filters, and builds trust with Mailbox Providers (MPs).
What is Email Warm-Up?
Email warm-up is the process of gradually increasing the volume of emails sent from your domain and IP addresses over time. This helps ISPs evaluate your sending behavior and builds a solid sender reputation. A proper warm-up ensures your emails land in recipients' inboxes instead of their spam folders.
There are two main types of emails to consider during a warm-up:
Transactional Emails: High-priority emails like receipts, password resets, and account notifications.
Bulk Marketing Emails: Newsletters, promotions, and other non-essential communications.
Why Warm-Up is Critical
Without a proper warm-up, MPs might perceive sudden high-volume sending as spammy behavior, resulting in:
Increased bounce rates.
Low inbox placement.
Poor sender reputation.
Higher chances of being blacklisted.
Warm-Up Strategies Based on Email Type
For e.g. to scale to 1 million emails per day, we recommend two distinct warm-up approaches:
1. Aggressive Warm-Up for Transactional Emails
Transactional emails are time-sensitive and expected by recipients, making them ideal for a faster warm-up process. Since these emails generally have high open and engagement rates, ISPs are more likely to trust them.
Ensure that you send your campaigns in batches, with at least one hour between each batch.
Day | Emails/Day | Total Emails | Key Actions |
Day 1 | 5.000 | 5.000 | Start with the most critical, high-priority transactional recipients. Monitor open rates. |
Day 2 | 7.000 | 12.000 | Gradually increase volume, focusing on highly engaged users. |
Day 3 | 10.000 | 22.000 | Include additional transactional types, ensuring minimal bounces and complaints. |
Day 4 | 20.000 | 42.000 | Double the volume; closely monitor domain/IP reputation. |
Day 5 | 30.000 | 72.000 | Expand to a broader list while maintaining engagement (>20%). |
Day 6 | 55.000 | 127.000 | Continue gradual increases. Track open rates and spam complaints closely. |
Day 7 | 85.000 | 212.000 | End of Week 1. Scale up as reputation stabilizes. |
Day 8 | 125.000 | 337.000 | Begin Week 2. Monitor IP/domain health using tools like Google Postmaster Tools. |
Day 9 | 175.000 | 512.000 | Increase further; keep bounce rates below 2%. |
Day 10 | 275.000 | 787.000 | Larger increments possible as engagement metrics remain stable. |
Day 11 | 400.000 | 1.187.000 | Test sending at higher volumes while ensuring consistency in delivery. |
Day 12 | 650.000 | 1.837.000 | Scale aggressively but monitor reputation metrics closely. |
Day 13 | 800.000 | 2.637.000 | Stabilize performance and resolve any deliverability issues. |
Day 14 | 1.000.000 | 3.637.000 | Full capacity reached. Monitor and maintain sender reputation. |
2. Less Aggressive Warm-Up for Bulk Mailers
Bulk emails require a more cautious approach because ISPs scrutinize them more closely for spam-like behavior. The audience's engagement is often lower, which makes building reputation slower.
Ensure that you send your campaigns in batches, with at least one hour between each batch. Gradually increase the batch size throughout the week, adhering to the limits outlined in the schedule below.
Plan for Bulk Marketing Emails:
Week | Emails/Day | Total Emails/Week | Key Actions |
Week 1 | 5.000 | 20.000 | Start with the most engaged recipients. Monitor bounce and complaint rates. |
Week 2 | 10.000 | 40.000 | Gradually expand to moderately engaged users. Maintain >20% open rates. |
Week 3 | 25.000 | 100.000 | Focus on list quality. Include new segments cautiously. |
Week 4 | 50.000 | 200.000 | Double volume; monitor ISP feedback and domain/IP reputation. |
Week 5 | 100.000 | 400.000 | Expand further with a focus on maintaining engagement metrics. |
Week 6 | 200.000–350.000 | 800.000 – 1.400.000 | Introduce less active segments. Scale cautiously, monitoring every send. |
Week 7 | 500.000 | 2.000.000 | Achieve half target volume. Optimize engagement with refined content and segmentation. |
Week 8 | 800.000 | 3.200.000 | Scale aggressively while ensuring list hygiene and reputation stability. |
Week 9+ | 1.000.000 | 4.000.000 | Full capacity. Regularly clean lists and ensure continuous monitoring. |
Tips for Successful Warm-Up
Authenticate Your Emails:
Set up SPF, DKIM, and DMARC to authenticate your emails and boost credibility with ISPs. Proper authentication prevents your messages from being flagged as suspicious.
Monitor Engagement Metrics:
Open rates: Aim for rates above 20%.
Spam complaints: Keep complaints below 0.3%.
Bounce rates: Ensure hard bounces are under 2%.
Use High-Quality Email Lists:
Avoid purchased or outdated lists, as they often lead to high bounce and complaint rates.
Use clean, segmented lists with active recipients to ensure higher engagement.
Implement Captcha and Double Opt-In for Collection Forms:
Captcha: Add a bot detection tool, like Google reCAPTCHA, to prevent spam or fake sign-ups.
Double Opt-In: Require subscribers to verify their email address by clicking a confirmation link sent to their inbox. This ensures only valid and willing recipients join your list.
Test Email Content:
Avoid using spammy words (e.g., “free,” “urgent,” or “guaranteed”).
Craft engaging subject lines and ensure content aligns with your audience's preferences.
Leverage Feedback Tools:
Use tools like Google Postmaster Tools, Microsoft SNDS, and other monitoring platforms to track sender reputation, delivery performance, and inbox placement.
Be Consistent:
Maintain a regular sending schedule to build predictability with ISPs. Sudden spikes in volume can harm your reputation.