What Is Email Warm-Up?

What Is Email Warm-Up?

Email warm-up is the process of gradually increasing sending volume from a new IP address or domain to establish a positive sender reputation with Internet Service Providers (ISPs) and email providers. It's a critical step when starting to send emails from new infrastructure.

When you use a new IP address or domain, ISPs have no sending history to evaluate your reputation. They treat new senders cautiously, which can result in higher spam filtering rates. Warm-up helps build reputation gradually, demonstrating that you're a legitimate sender who follows best practices.

During warm-up, you start with small sending volumes to highly engaged recipients and gradually increase volume over several weeks while monitoring performance metrics. This process helps establish trust with ISPs and improves deliverability over time.

Why Is Email Warm-Up Important?

1. New IPs Have No Reputation

New IP addresses have zero sending history. ISPs don't know if you're a legitimate sender or a spammer, so they apply stricter filtering. Warm-up builds positive reputation gradually.

2. Prevents Immediate Filtering

Sending large volumes immediately from a new IP often results in high spam filtering rates. Gradual warm-up helps avoid this by demonstrating good sending behavior.

3. Builds Sender Reputation

Warm-up helps establish positive reputation signals: low bounce rates, high engagement, minimal complaints. Monitor your domain health during warm-up.

4. Prevents Blacklisting

Aggressive sending from new IPs can trigger blacklisting. Warm-up reduces this risk by starting conservatively and building reputation safely.

5. Improves Long-Term Deliverability

Properly warmed IPs achieve better long-term deliverability rates than IPs that start with high volumes immediately.

6. Establishes Trust

Gradual warm-up demonstrates to ISPs that you're a responsible sender who follows best practices and respects recipient preferences.

How Email Warm-Up Works

Email warm-up works by gradually introducing your new IP or domain to ISPs while demonstrating positive sending behavior. ISPs track various signals to build your reputation profile.

Reputation Signals ISPs Track

• Bounce Rates: Low bounce rates indicate good list quality
• Spam Complaints: Minimal complaints show recipients want your emails
• Engagement: High open and click rates signal wanted emails
• Sending Patterns: Consistent, gradual increases show responsible sending
• Authentication: Proper SPF, DKIM, and DMARC improve reputation
• Blacklist Status: Staying off blacklists is essential

As you send emails during warm-up, ISPs evaluate these signals and gradually build your reputation score. Positive signals improve reputation, while negative signals (bounces, complaints) hurt it.

The Warm-Up Process

Week 1: Initial Phase

Start with 50-100 emails per day to your most engaged recipients. Focus on:

• Sending to verified, highly engaged subscribers
• Ensuring proper email authentication
• Testing emails with our email testing tool before sending
• Monitoring bounce rates and engagement

Weeks 2-4: Gradual Increase

Gradually increase volume by 20-30% each week if metrics are positive:

• Week 2: 150-200 emails/day
• Week 3: 300-500 emails/day
• Week 4: 500-1000 emails/day

Weeks 5-8: Continued Growth

Continue increasing volume while monitoring performance:

• Week 5: 1,000-2,000 emails/day
• Week 6: 2,000-5,000 emails/day
• Week 7: 5,000-10,000 emails/day
• Week 8: 10,000+ emails/day (based on needs)

Important Considerations

• Only increase volume if metrics are positive
• If bounces or complaints increase, reduce volume
• Maintain consistent sending patterns
• Continue testing emails before sending
• Monitor domain health regularly

Best Practices for Email Warm-Up

1. Start with Engaged Recipients

Begin warm-up by sending to your most engaged subscribers—those who regularly open, click, and interact with your emails. High engagement signals help build positive reputation.

2. Implement Email Authentication

Ensure proper SPF, DKIM, and DMARC before starting warm-up. Use our authentication checker to verify.

3. Test Before Sending

Always test your emails before sending during warm-up. Check spam scores with SpamAssassin and verify content quality.

4. Use Clean Lists

Only send to verified, opt-in recipients. Avoid purchased lists or unverified addresses that could cause high bounce rates.

5. Monitor Metrics Closely

Track bounce rates, spam complaints, engagement rates, and blacklist status. Adjust warm-up pace based on performance.

6. Maintain Consistency

Send consistently rather than in bursts. Irregular patterns can raise flags with ISPs.

7. Be Patient

Warm-up takes time—typically 4-8 weeks. Rushing the process can damage reputation and hurt long-term deliverability.

Monitoring Warm-Up Progress

Regular monitoring during warm-up is essential to ensure the process is working correctly and to identify issues early.

Key Metrics to Monitor

• Bounce Rates: Should stay low (under 2% for hard bounces)
• Spam Complaints: Should be minimal (under 0.1%)
• Open Rates: Should be high (indicates engagement)
• Click Rates: Positive engagement signal
• Blacklist Status: Check regularly with domain health check
• Inbox Placement: Monitor deliverability rates

Tools for Monitoring

• Domain Health Check: Monitor blacklist status and overall health
• Authentication Checker: Verify SPF, DKIM, DMARC
• Email Testing Tool: Check spam scores and deliverability
• SpamAssassin Test: Evaluate spam filter scores

Adjusting Warm-Up Pace

If metrics are positive, you can gradually increase volume. If you see issues:

• Reduce sending volume
• Focus on most engaged recipients
• Review and fix content issues
• Verify authentication is working
• Check for blacklist issues