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Warm-Up Your Domains

I. What is Domain Warm-up?​

Domain Warm-up is the process of gradually increasing sending volume before full-scale email sending, to build trust with email service providers for your sending domain.

In simple terms:

  • 👉 Do NOT send in large volumes from day one
  • 👉 Start small, then scale up to build reputation step by step

II. Why is Domain Warm-up Mandatory?​

Email service providers (ISPs) assign a reputation score to every sending domain, such as:

  • Google (Gmail)
  • Microsoft (Outlook / Hotmail)
  • Yahoo (Yahoo Mail)

If you:

  • Use a newly registered domain
  • Resume sending after a long silence
  • Send a huge batch suddenly

👉 You will likely be classified as a spammer.

Risks of Skipping Warm-up​

  • ❌ Mass delivery to spam folder
  • ❌ Rapid domain reputation decline
  • ❌ Throttling or blocking by ISPs
  • ❌ Difficult to recover later

III. When is Warm-up Required?​

Domain warm-up is required in these scenarios:

  • 🆕 Newly registered domain (especially < 90 days old)
  • 💤 Long inactivity (7–30+ days without sending)
  • 🔄 Switching email service providers or IPs
  • 📈 Preparing to scale up sending volume
  • 🧪 Launching a new subdomain (e.g., marketing.xxx.com)

IV. Core Principles of Warm-up​

1. Start Small​

Begin with a low initial volume, for example:

Day 1: 50–200 emails

2. Steady Growth​

Increase volume gradually each day:

20% – 50% growth per day

Avoid:

  • Sudden doubling
  • Irregular fluctuations

3. Prioritize High-quality Users​

During warm-up, send only to:

  • Recently active users
  • Users who opened/clicked before
  • Confirmed subscribers

Avoid:

  • Cold lists
  • Purchased email lists

4. Control ISP Distribution​

Do not concentrate emails on a single ISP.

👉 Distribute evenly across ISPs.

5. Maintain Consistency​

Send every day. Avoid:

  • Sending on one day and stopping the next
  • Large swings in volume

V. Sample Warm-up Schedule (Reference)​

Below is a typical 14‑day domain warm-up rhythm:

DayDaily Volume
Day 1100
Day 2150
Day 3220
Day 4300
Day 5450
Day 6650
Day 7900
Day 81200
Day 91600
Day 102200
Day 113000
Day 124000
Day 135500
Day 147000+

👉 Adjust based on your target scale.

VI. Metrics to Monitor During Warm-up​

1. Delivery Rate​

  • Whether emails are accepted by the server
  • Healthy target: ≥ 95%

2. Open Rate​

  • Reflects user engagement
  • Should be high during warm-up (20%+)

3. Complaint Rate​

  • Whether users mark as spam
  • Recommended: < 0.1%

4. Bounce Rate​

  • Percentage of invalid addresses
  • Recommended: < 2%

VII. Warm-up Differences by Domain Type​

1. Transactional Domain​

Characteristics:

  • User-triggered
  • High engagement

Strategy:

  • Can warm up slightly faster
  • Focus on stability

2. Marketing Domain​

Characteristics:

  • Bulk sending
  • Higher complaint risk

Strategy:

  • Must strictly control growth
  • Heavily dependent on list quality

VIII. Common Warm-up Mistakes​

1. Starting with Huge Volume​

Day 1: Send 10,000+ emails directly

👉 High chance of immediate spam folder placement.

2. Poor List Quality​

  • Cold lists
  • Non-subscribed users

👉 Quickly damages reputation.

3. Unstable Sending​

  • Erratic volume
  • Intermittent sending

👉 ISPs cannot build consistent trust.

4. Chaotic Multi-domain Warm-up​

👉 Warm domains one by one, not all at once.

IX. When is Warm-up Complete?​

Warm-up is considered complete when:

  • Inbox deliverability stabilizes at 85%+
  • Open rate remains consistent
  • Complaint rate stays low
  • Sending volume can be increased stably

X. Recommendations After Warm-up​

  • Maintain consistent sending
  • Avoid sudden volume spikes
  • Clean your list regularly
  • Continuously optimize content quality

XI. Summary​

The essence of domain warm-up is: Prove to ISPs that you are a trustworthy sender.

Through stable, gradual, high-quality sending behavior, you build domain reputation—this is the key to ensuring emails land in the inbox.