Warmup is the process of gradually increasing email volume from a new IP address or domain to build sender reputation. Rushing this process triggers spam filters. Here is what to expect for different scenarios.
Warmup Timelines by Volume
| Target Monthly Volume | Typical Warmup Period |
|---|---|
| Under 25,000 | 2-3 weeks |
| 25,000 - 100,000 | 4-5 weeks |
| 100,000 - 500,000 | 6-8 weeks |
| 500,000 - 1,000,000 | 8-10 weeks |
| Over 1,000,000 | 10-12 weeks |
What Affects Warmup Duration
Target Volume
The higher your eventual sending volume, the longer warmup takes. You cannot safely jump from zero to 100,000 daily emails. Each volume level needs time to establish reputation.
Engagement Quality
High engagement (opens, clicks) during warmup signals wanted email. This can accelerate the process. Poor engagement extends it.
List Quality
Clean lists with valid, engaged addresses warm up faster. Dirty lists with bounces and complaints extend warmup or cause failure.
Provider Mix
Different providers have different thresholds. Gmail is typically more sensitive to new senders than others. A list heavy on Gmail addresses may require more gradual warmup.
IP vs Domain Warmup
IP Warmup
New IP addresses have no sending history. Mailbox providers track IP behavior over time. IP warmup establishes that your IP sends legitimate email.
Domain Warmup
New domains also need reputation building. Even on a warm IP, a new domain faces scrutiny. Domain warmup establishes your brand's sending credibility.
Both Together
If you have both a new IP and new domain, warmup takes longer because you are building two reputations simultaneously. Consider using an established domain on a new IP, or vice versa, to reduce risk.
Cannot Rush Warmup
There is no shortcut. Attempting to accelerate warmup by increasing volume too quickly will damage reputation and may result in blocking. The timeline exists because reputation systems need time to observe consistent good behavior.
Sample 6-Week Warmup Timeline
| Week | Daily Volume | Focus |
|---|---|---|
| Week 1 | 200-500 | Most engaged subscribers only |
| Week 2 | 500-1,500 | Expand to recent engagers |
| Week 3 | 1,500-5,000 | Monitor metrics closely |
| Week 4 | 5,000-15,000 | Add more of list if metrics good |
| Week 5 | 15,000-40,000 | Approaching normal volume |
| Week 6 | 40,000+ | Full volume if healthy |
Signs Warmup Is Going Well
- Bounce rates under 2%
- Complaint rates under 0.1%
- Good inbox placement (test with seed lists)
- No throttling or deferral messages
- Engagement rates consistent with expectations
Signs Warmup Is Struggling
- Increasing bounce rates
- Complaints above 0.1%
- Messages deferred with "try again later"
- Poor inbox placement
- Blocklist entries
If you see these signs, slow down. Reduce volume and focus on your most engaged recipients. Do not push forward hoping it will resolve.
After Warmup
Completing warmup does not mean you can send carelessly:
- Maintain consistent sending patterns
- Continue monitoring metrics
- Keep complaint rates low
- Avoid sudden large volume increases