IP and Domain Warming Guide

Decide what needs warming

You need warming when a sending identity has little or no recent reputation.

The more critical the traffic, the more conservative the ramp should be.

Start with the best recipients

Warm-up traffic should go to users who expect the mail and are likely to engage.

Good early segments:

1. Recent active users.
2. Paying customers.
3. Users who requested the message.
4. Internal test accounts at major mailbox providers.

Avoid stale imports, purchased lists, and broad reactivation campaigns during the first phase.

Use a provider-aware ramp

Different mailbox providers react differently. Track volume and outcomes by recipient domain:

Pause or slow the ramp if Gmail, Outlook, Yahoo, or a large corporate domain starts deferring mail.

Understand automatic phase advancement

Postscale checks advancement once daily at 01:00 UTC. Time in a phase and healthy delivery metrics are required, along with average daily sending volume of at least 50% of the phase's daily limit. For a Phase 1 limit of 1,500 recipients/day, that means an average of 750 recipients/day.

The evaluation counts accepted recipients from the previous seven complete UTC days plus today's sends so far, then divides by seven. Days without sends count too. A domain sending below this volume can stay in Phase 1 beyond two weeks even with excellent delivery metrics.

For low-volume transactional mail, keep sending within your current limits. Do not generate extra mail to reach a threshold. If you need higher limits for planned growth, support can review your sending history and ramp-up plan. See the warming requirements and support-review options.

Watch warning signals

Slow down when you see:

1. Hard bounce rate rising above normal baseline.
2. Spam complaints.
3. Repeated 4xx deferrals from the same provider.
4. DKIM or DMARC failures after a DNS change.
5. A sudden drop in engagement on non-critical mail.

Do not compensate for deferrals by pushing more mail. That usually makes reputation worse.

Keep critical mail separate

During a migration or warm-up, keep password resets, login codes, invoices, and security alerts on the most reliable stream available.

If you are moving from another provider, run parallel sending for a short period:

1. New low-risk transactional messages through Postscale.
2. Critical account access mail on the established path.
3. Gradual cutover once delivery signals are stable.

The email API migration guide includes a staged cutover pattern.