IP & Domain Warming

Guide to warming your domain and IP for optimal email deliverability.

When you start sending from a new domain or IP address, mailbox providers (Gmail, Microsoft, Yahoo) have no history to judge your reputation. Warming is the process of gradually increasing your sending volume so these providers learn to trust your email.

Why Warming Matters

Sending a large volume of email from an unknown domain triggers spam filters and can result in:

Emails landing in spam folders
Temporary deferrals (greylisting)
Outright rejections
Long-term reputation damage that's hard to reverse

Warming builds a positive sending history so providers deliver your email to the inbox.

How Postscale Warming Works

Postscale uses a 4-phase warming system that automatically manages your sending volume. After your domain's DNS is verified, warming starts automatically.

Warming Phases

Phase	Timeline	Daily Limit	What Happens
Phase 1	Week 1-2	50 - 1,500	Initial low-volume sends to establish reputation
Phase 2	Week 3-4	2,000 - 10,000	Moderate volume with expanded ISP distribution
Phase 3	Week 5-6	15,000 - 60,000	High volume with reputation monitoring
Phase 4	Week 7-8	100,000 - 200,000	Near-production volume before graduation
Warmed	Ongoing	Unlimited	Fully warmed, no restrictions

Automatic Advancement

Postscale automatically advances you to the next phase when:

You've spent the minimum number of days in the current phase
Your delivery metrics meet the required thresholds (delivery rate, bounce rate, complaint rate)
Your average daily sending volume reaches at least 50% of your current phase's daily limit

Advancement is checked once daily at 01:00 UTC. Meeting the requirements during the day makes your domain eligible for the next check; all requirements must still pass at that time. The timelines above are estimates, not guaranteed advancement dates.

The evaluation uses accepted recipient counts from the previous seven complete UTC days plus today's sends so far. Average daily volume is that total divided by seven. Days without sends still count in the average. Volume counts recipients, so a message accepted for three recipients contributes three to the total.

For example, with a Phase 1 daily limit of 1,500 recipients, automatic advancement requires an average of 750 recipients/day, or 5,250 accepted recipients in the evaluation window. With the standard Phase 1 configuration, you also need at least 14 days in the phase, a delivery rate of at least 95%, a bounce rate no higher than 2%, and a complaint rate no higher than 0.1%. Your dashboard shows your current limits and any advancement blockers.

A domain with 147 accepted recipients in the window averages 21 per day. Even after 18 days with healthy delivery metrics, it remains in Phase 1 because it has not met the volume requirement. Domains with no sending activity also remain in their current phase.

Low-volume senders

You can continue sending within your current phase limits for as long as needed. Remaining in a phase because of low volume does not mean your delivery metrics are poor. Do not send extra or unwanted email just to reach the advancement threshold.

If your normal volume is below the threshold and you need higher limits, contact support with your domain, recent sending history, and expected future volume. Support can review your ramp-up plan and whether a manual advancement is appropriate; it is not automatic or guaranteed.

Automatic Start After DNS Verification

When you verify your domain's DNS records (SPF and/or DKIM), Postscale automatically starts warming. You don't need to do anything extra: just start sending within your phase limits.

You can also manually start warming via the API. See the Warming API reference.

Volume Limits During Warming

While warming is active, Postscale enforces daily, hourly, and per-minute rate limits based on your current phase. When you send an email, the API response includes your remaining limits:

{
  "message_id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890@yourapp.com",
  "status": "queued",
  "warming_phase": "phase_1",
  "remaining_today": 1500,
  "remaining_this_hour": 100
}

If you exceed the limit, sends are rejected until the next period.

Best Practices During Warming

Send to engaged recipients first

Start with your most active users: people who open and click your emails. High engagement signals to providers that your email is wanted.

Maintain consistent volume

Send steadily throughout each phase rather than in large bursts. Consistent patterns look more trustworthy to providers.

Keep your lists clean

Remove invalid addresses and hard bounces promptly. A high bounce rate during warming can stall advancement or damage your reputation.

Use proper authentication

Ensure SPF, DKIM, and DMARC are all configured correctly before warming. See the Domain Setup guide.

Monitor your metrics

Watch your delivery rate, bounce rate, and complaint rate in the dashboard. Postscale pauses advancement if metrics fall below thresholds, giving you time to investigate.

Don't skip warming

Skipping warming by sending high volumes immediately from a new domain can severely damage your sender reputation. Always complete the full warming schedule before sending at production volume.

Monitoring Warming Progress

In the Dashboard

Navigate to Domains and click on a domain to see its warming status, current phase, daily limits, and delivery metrics.

Via the API

Use the warming endpoints to check status programmatically:

GET /v1/domains/:id/warming: current status and limits
GET /v1/domains/:id/warming/history: phase transition history
POST /v1/domains/:id/warming/pause: pause warming
POST /v1/domains/:id/warming/resume: resume warming

See the full Warming API reference for request/response details.

Pausing and Resuming

If you need to pause warming (e.g., to investigate a bounce spike), you can do so from the dashboard or via the API. When you resume, you return to the same phase: no progress is lost.

FAQ

How long does warming take?

The phase schedule is an estimate. Advancement depends on time in phase, delivery metrics, and sending volume, so a domain can remain in a phase longer when it sends below the required volume or its delivery metrics need improvement.

Can I send during warming?

Yes! Warming doesn't block sending: it limits your daily volume. Send within the phase limits shown in your dashboard.

What if I already have a good domain reputation?

If your domain has an established sending history elsewhere, warming still applies when sending through Postscale for the first time. The process helps establish your reputation on Postscale's infrastructure specifically.

What happens if my metrics drop?

Postscale pauses phase advancement until metrics recover. You can still send within your current phase limits. Check the dashboard for specific blockers.