Domain Warmup
Build sender reputation for new domains with automated warmup. Improve deliverability and avoid spam folders.
Build a strong sender reputation by gradually increasing email volume.
New domains should always go through warmup before high-volume sending. Skipping this step is the #1 cause of deliverability problems.
Why Warmup Matters
When you start sending from a new domain, inbox providers (Gmail, Outlook, Yahoo) have no history to evaluate you. To protect their users, they're suspicious of high-volume traffic from unknown senders.
Warmup proves legitimacy by starting small and gradually increasing volume, showing consistent sending patterns and healthy metrics over time.
How It Works
Automated Ramp-Up
Transmit handles warmup automatically:
- Start small — Begin at 25 emails/day
- Gradual increase — Volume multiplies by 1.5x daily
- Health monitoring — Pauses automatically if issues arise
- Target reached — Completes when you hit your target limit
Default Settings:
| Setting | Default |
|---|---|
| Starting limit | 25 emails/day |
| Target limit | 5,000 emails/day |
| Ramp-up factor | 1.5x daily |
| Ramp-up period | 28 days |
Health Monitoring
Transmit monitors bounce and complaint rates in real-time:
| Metric | Warning | Critical (Auto-Pause) |
|---|---|---|
| Bounce rate | > 3% | > 5% |
| Complaint rate | > 0.05% | > 0.1% |
If critical thresholds are exceeded, warmup pauses automatically to protect your reputation.
Setup
Enable Warmup
- Go to Domains in the dashboard
- Click on your verified domain
- Navigate to Warmup settings
- Configure your target daily limit
- Click Enable Warmup
Monitor Progress
The warmup dashboard shows:
- Current daily limit
- Progress toward target
- Health status (healthy, warning, critical)
- Bounce and complaint rates
Warmup States
| Status | Meaning |
|---|---|
| Inactive | Warmup not started |
| Active | Currently warming up |
| Paused | Stopped due to health issues or manual pause |
| Completed | Target limit reached |
Pause Reasons
If warmup pauses, you'll see why:
| Reason | Cause |
|---|---|
| Manual | You paused it |
| High bounce rate | Bounce rate exceeded 5% |
| High complaint rate | Complaint rate exceeded 0.1% |
Troubleshooting
Warmup Paused - High Bounce Rate
Causes:
- Sending to invalid addresses
- Old list that hasn't been cleaned
Solutions:
- Enable Email Validation to catch bad addresses
- Remove addresses that bounced
- Resume warmup once list is cleaned
Warmup Paused - High Complaint Rate
Causes:
- Sending to people who didn't opt in
- Content not matching expectations
Solutions:
- Only email people who explicitly signed up
- Make unsubscribe easy to find
- Resume warmup after addressing the issue
Best Practices
- Clean your list before starting warmup
- Send to engaged users first during warmup (recent signups, active users)
- Monitor daily during the warmup period
- Don't skip warmup even if you're in a hurry
Related
- Domain Verification — Set up your sending domain
- Email Validation — Prevent bounces automatically
- Suppressions — Manage bounced addresses