Deliverability

Domain Warmup

Automated IP and domain warming with exponential ramp-up. Auto-pause on high bounce rates protects your sender reputation.

How it works

1

Enable warmup

Turn on warmup for any domain. Set your starting volume, target volume, and growth factor.

2

Exponential ramp

Daily limits increase automatically using the formula: limit = start × factor^(day-1). Default 1.5x doubles volume every ~2 days.

3

Auto-pause protection

If bounce or complaint rates exceed thresholds, sending pauses automatically to protect your domain reputation.

4

Reach full volume

Once you hit your target daily limit with healthy metrics, warmup completes and you're ready for full-scale sending.

Capabilities

Configurable Parameters

Set starting limit (default 25), target limit (default 5,000), and growth factor (default 1.5x). Tune for your sending patterns.

Auto-Pause on Issues

Campaigns automatically pause when daily warmup limits are reached or when bounce/complaint rates spike. Resume the next day.

Per-Domain Tracking

Each domain warms up independently. Track daily sends, current limits, and days remaining for every sending domain.

Midnight Reset

Counters reset at midnight UTC. The scheduler advances warmup day and increases limits automatically , no manual intervention.

Warmup Algorithm

javascript
// Transmit's production warmup algorithm
function calculateDailyLimit(
  startingLimit,  // e.g., 25
  targetLimit,    // e.g., 5000
  rampUpFactor,   // e.g., 1.5
  day             // current warmup day
) {
  // Exponential growth: limit = start × factor^(day-1)
  const calculated = Math.round(
    startingLimit * Math.pow(rampUpFactor, day - 1)
  );
  // Cap at target limit
  return Math.min(calculated, targetLimit);
}

// Example progression with defaults:
// Day 1:  25 emails
// Day 2:  37 emails
// Day 3:  56 emails
// Day 5:  126 emails
// Day 10: 961 emails
// Day 14: 4,860 emails → capped at 5,000

Related features

Webhooks

Email Webhooks

Real-time notifications for email events. Get instant delivery, bounce, open, click, and complaint data pushed to your endpoint.

Deliverability

Multi-Tenant Reputation Isolation

Per-customer sending reputation. Your deliverability is never affected by other senders on the platform.

Frequently Asked Questions

Why do I need to warm up a domain?
ISPs track sending patterns for new domains and IPs. Sending too much too fast from a cold domain triggers spam filters and rate limiting. Warmup gradually builds trust with inbox providers by demonstrating consistent, legitimate sending patterns.
How long does warmup take?
With default settings (start: 25, target: 5,000, factor: 1.5x), warmup completes in about 14 days. Higher growth factors finish faster but are riskier. Lower factors are safer but slower. Use our Warmup Calculator tool to plan your schedule.
What happens if I hit the daily limit mid-campaign?
The campaign automatically pauses with status 'warmup_paused'. It resumes the next day when the daily counter resets and limits increase. No emails are lost , they're queued for the next sending window.
What triggers auto-pause for reputation issues?
Transmit monitors bounce and complaint rates in real-time. If rates exceed safe thresholds (typically 5% bounce or 0.1% complaint), sending pauses automatically to prevent further reputation damage.
Can I warm up multiple domains at once?
Yes. Each domain has independent warmup state. You can warm up your transactional domain (app.example.com) and marketing domain (mail.example.com) simultaneously with different settings.
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