What is domain warmup?
Domain warmup is the process of gradually increasing email volume from a new domain to build sender reputation with ISPs. When you register a new domain or start sending from one that has no email history, ISPs have no data to judge whether you're a legitimate sender or a spammer.
By starting with small volumes and slowly ramping up, you demonstrate consistent, legitimate sending behavior. ISPs track your bounce rate, complaint rate, and engagement metrics during this period to establish your domain's reputation score.
Before you start: authentication first
Never send a single email before your authentication is configured correctly:
- SPF record — authorizes your sending servers
- DKIM signing — cryptographically signs your emails
- DMARC policy — tells ISPs what to do with unauthenticated email (start with
p=none)
Sending without authentication during warmup is worse than not warming up at all. ISPs will immediately flag your domain as suspicious.
Warmup schedule
This schedule works for most use cases. Adjust based on your target daily volume:
| Week | Daily Volume | Recipients | Notes |
|---|---|---|---|
| 1 | 50-100 | Most engaged only | Monitor every metric daily |
| 2 | 200-500 | Engaged recipients | Check Google Postmaster Tools |
| 3 | 1,000-2,000 | Add moderately engaged | Pause if bounce rate > 2% |
| 4 | 5,000-10,000 | Broader audience | Watch complaint rate closely |
| 5-6 | 20,000-50,000 | Full list minus unengaged | Should see stable inbox placement |
| 7-8 | Target volume | Full list | Warmup complete |
What to send during warmup
- Send your normal transactional emails (welcome, receipts, notifications) — these have the highest engagement
- Avoid promotional or marketing emails in the first 2 weeks
- Keep content consistent — don't switch between completely different email types
- Include a clear unsubscribe link in every email
- Use the same From address consistently
Metrics to monitor during warmup
- Bounce rate — must stay below 2%. Pause and clean your list if it spikes.
- Complaint rate — must stay below 0.1%. This is the most damaging metric.
- Open rate — should be above 20% during warmup (you're sending to engaged users).
- Delivery rate — should be above 95%. Anything lower indicates throttling.
Check Google Postmaster Tools daily during warmup for Gmail-specific reputation data.
When to pause warmup
Stop sending and investigate if any of these occur:
- Bounce rate exceeds 5% on any single day
- Complaint rate exceeds 0.1%
- You see a sudden drop in open rates (possible spam folder placement)
- You receive a blocklist notification
- Google Postmaster Tools shows "Bad" domain reputation
Fix the underlying issue before resuming. When you restart, go back one step in the volume schedule.
Warmup with RelayPost
RelayPost simplifies warmup with:
- Automatic DKIM/SPF configuration during domain verification
- Real-time delivery monitoring to catch issues early
- Automatic bounce and complaint suppression
- High-reputation sending infrastructure as your baseline
Related guides
Frequently asked questions
Why do I need to warm up a new domain?
New domains have zero sending reputation. ISPs are cautious about unknown senders and may throttle or spam-filter your emails. Warming up gradually builds trust by demonstrating consistent, legitimate sending behavior over time.
How long does domain warmup take?
A typical warmup takes 4-8 weeks. The exact timeline depends on your target volume. If you're sending under 1,000 emails/day, warmup is faster (2-3 weeks). For high-volume senders (50K+/day), plan for 6-8 weeks of gradual ramp-up.
Can I skip warmup if I use a shared IP?
You still need to warm up your domain reputation, even on shared IPs. While shared IPs have existing IP reputation, ISPs increasingly weight domain reputation independently. A new domain on a warm IP still needs gradual volume increases.
What happens if I send too much too fast?
ISPs will throttle your delivery (temporary deferrals), route emails to spam, or in severe cases, block your domain entirely. Recovering from a bad warmup is harder than doing it right the first time — it can take weeks to rebuild trust.
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