Email Infrastructure Warm-up Guide
Purpose

This guide explains why and how to warm up a new email infrastructure (e.g., AWS SES, new IPs, or new sending provider) to protect deliverability and domain reputation during migration or scaling.

Why Warming Up Matters

Even if your domain is trusted, email deliverability depends on two separate reputations:

  • Domain reputation – built from your domain’s sending history, content, and user engagement.

  • IP reputation – associated with the mail server or provider sending your messages.

When you move to a new platform like AWS SES or new IPs, mailbox providers (Gmail, Outlook, Yahoo, etc.) see that as a new sender. They test and throttle traffic until consistent, low-complaint patterns emerge.

Warm-up gradually establishes trust between your domain and the new sending IPs. It prevents throttling, soft bounces, or spam filtering during transitions.

When Warming Is Needed

Scenario

Warm-up Required?

Reason

New domain

✅ Yes

No prior reputation with mailbox providers

Same domain, new provider (e.g., Postfix → SES)

✅ Yes

New IPs and DKIM signatures look different to ISPs

Shared IP pool (SES default)

🟡 Recommended

Still new sending pattern for your domain

Dedicated IPs

🔥 Critical

IPs start with zero reputation

Warm-up Strategy

The goal is to increase sending volume gradually over 2–3 weeks while keeping bounce and complaint rates extremely low (<0.1%).

Step-by-step

  1. Start small: Send 5–10% of your total daily volume via the new system.

  2. Prioritize low-risk messages: Password resets, signup confirmations, and system alerts perform best.

  3. Monitor every day: Track bounces, complaints, and throttling.

  4. Increase volume slowly: Double every few days as long as metrics remain clean.

  5. Reach 100% traffic after 10–15 days.

Example Warm-up Schedule (1.2M Emails/Month)

Day Range

Approx. % of Volume

Daily Volume

Notes

Days 1–3

5–10%

2,000–4,000/day

Initial trust-building, low-risk messages only

Days 4–7

20–30%

8,000–12,000/day

Expand to moderate-importance messages

Days 8–14

50–70%

20,000–28,000/day

Gradual scaling, monitor deliverability closely

Day 15+

100%

40,000+/day

Full cutover if stable and bounce <0.1%

What to Monitor

  • Bounce rate: Should stay below 1%; aim for <0.3%.

  • Complaint rate: Should stay below 0.1%.

  • Delivery latency: Sudden delays can signal throttling.

  • Inbox placement: Use test mailboxes to ensure messages don’t land in spam.

Best Practices

  • Authenticate properly: SPF, DKIM, and DMARC must be valid before sending.

  • Use consistent sending patterns: Volume, frequency, and content type should stay stable.

  • Segment sending types: Start with transactional, later add bulk or marketing.

  • Avoid sudden spikes: No more than 2× increase per 2–3 days.

  • Monitor reputation: Use SES metrics, CloudWatch, or tools like GlockApps or Postmaster Tools.

Key Takeaway

Warming up is not about email volume — it’s about building trust with mailbox providers. A gradual ramp-up ensures your domain’s reputation transfers cleanly to new infrastructure without delivery issues.

Quote: “Warm-up is the bridge between infrastructure change and inbox trust — skip it, and even perfect emails end up ignored.”