What is Warming Up?
Warming up is the process of gradually increasing the volume of email sent from a new IP address or domain over a period of several weeks. This helps to establish a positive sending reputation with ISPs.
Why is it Necessary?
If you start sending a high volume of email from a "cold" (new) IP/domain, ISPs will view it as suspicious behavior typical of spammers. They will likely block your emails or send them to the spam folder.
The Warm-up Schedule
A typical warm-up schedule looks like this (daily volume):
- Day 1: 50 emails
- Day 2: 100 emails
- Day 3: 500 emails
- Day 4: 1,000 emails
- Day 5: 2,000 emails
- Week 2: Double volume every 2-3 days until target is reached.
Best Practices During Warm-up
- Target Your Best Users: Send to your most engaged subscribers first (those who opened/clicked recently). Their positive engagement will boost your reputation quickly.
- Monitor Bounce Rates: If bounces exceed 2-3%, pause and clean your list.
- Watch for Throttling: If ISPs start deferring your mail (4xx errors), slow down. You are moving too fast.
- Consistent Volume: Don't spike and crash. Try to maintain a steady flow.
Automated Warming
There are services that can automate this process by sending emails between a network of inboxes and automatically replying/marking as important. This can be a useful supplement to organic warming.