5 Email Warmup Mistakes That Kill Deliverability

Email warmup is the most important step in cold email infrastructure setup, and also the most commonly botched. Here are five mistakes that can tank your deliverability before you even start.

1. Sending Too Many Emails Too Fast

The number one mistake. New mailboxes have zero reputation. If you go from 0 to 50 emails per day on day one, email providers will flag you immediately. A proper warmup takes 2-4 weeks of gradually increasing volume.

2. Only Sending to One Provider

If all your warmup emails go to Gmail accounts, you're building reputation with Gmail but not with Outlook, Yahoo, or corporate mail servers. A good warmup tool distributes across providers.

3. Using Generic Warmup Content

Some warmup tools send nonsensical emails that look nothing like real business communication. Modern spam filters use content analysis. Your warmup emails should resemble actual business correspondence.

4. Not Monitoring During Warmup

Warmup isn't "set it and forget it." You need to monitor inbox placement rates throughout the process. If your placement drops below 80%, something is wrong and you need to adjust.

5. Stopping Warmup When You Start Sending

Warmup should continue alongside your cold outreach. Abruptly stopping warmup emails when you switch to campaign sends can signal to providers that something has changed, potentially hurting your reputation.

The Right Way

Start with 5-10 emails per day, increase by 5 every 2-3 days, monitor throughout, and keep warmup running even after you start campaigns. With patience, you'll build a rock-solid sender reputation.