How to warm up a new sending IP address step by step?

Updated: 28 September 2026 · Applies to: New sending IP addresses with Postfix 3.8 (Ubuntu 24.04) and 3.10 (Ubuntu 26.04)

A new IP address has no history. Mailbox providers watch how it behaves before they trust it. If you send a large volume from a brand-new address on the first day, receivers may delay or refuse the mail. Warming up means starting small and growing the volume step by step while the results stay good. This guide gives a plan you can adapt and the Postfix settings that keep you within it.

The principles

• Start with your best recipients: people who signed up recently and who open or click your mail.
• Grow only while the numbers are good. If complaints, bounces or delays rise, stop growing and stay at the current level or go back a step.
• Send regularly. Steady daily sending is better than a burst once a week.
• Keep the identity stable: the same domain, the same address and the same HELO name during the warm-up.
• Warm up each address separately. Every address has its own history.

Before you start

1. Authentication passes: SPF, DKIM and DMARC (How to write an SPF record for a server with several IP addresses?, How to set up DKIM signing with OpenDKIM and Postfix for several domains?, How to publish DMARC for your sending domains and tighten the policy safely?).
2. Reverse DNS and HELO name match (How to set reverse DNS (PTR) for many IP addresses and check forward-confirmed rDNS?, How to make Postfix send from a specific IP address with a matching HELO name?).
3. You have unsubscribe links and headers, and you process bounces (How to add a working unsubscribe link and one-click unsubscribe headers to your emails?, How to process bounces and spam complaints and keep a suppression list?).
4. You have a way to see results: Google Postmaster Tools for Gmail, and the bounce and complaint numbers from your own logs (How to test authentication and deliverability of your outgoing email?).

An example plan

These numbers are only a starting point. Mailbox providers publish no fixed schedule; adapt the plan to your list and the results you see.

1. Days 1 to 3: about 50 to 100 messages per day, to your most engaged recipients.
2. Days 4 to 7: about 200 to 500 per day.
3. Week 2: raise by about 50 percent every 2 or 3 days, for example 500, 750, 1,000, 1,500.
4. Week 3 and later: keep raising as long as the results are good, until you reach your normal volume. Bigger volumes usually take several weeks.

Spread each day's messages over the day instead of sending them in one block.

Check every day

• Delivery log: count status=sent, status=deferred and status=bounced (How to read Postfix logs and understand common SMTP error codes?). Many deferrals with "rate limited" or "try again later" mean: slow down.
• Complaints: Gmail wants the spam rate in Postmaster Tools below 0.3%, and Yahoo also asks for below 0.3%. Both recommend staying far below it.
• Bounce rate: remove hard bounces right away.

Limit the volume in Postfix

Use a separate transport for the address you are warming up (see How to make Postfix send from a specific IP address with a matching HELO name?) and add limits for it in /etc/postfix/main.cf. The name out2 is the transport name:

out2_destination_concurrency_limit = 2
out2_destination_rate_delay = 10s
out2_destination_recipient_limit = 5
out2_destination_concurrency_failed_cohort_limit = 10

With a recipient limit above 1, the rate delay is the time between deliveries to the same recipient domain, and each delivery can carry up to 5 recipients. So at most 5 recipients every 10 seconds go to one domain, about 0.5 per second (1,800 per hour). To the largest providers this is a comfortable start. The last line is needed with a rate delay, so that Postfix does not stop delivery to a destination after a single connection error. Loosen the numbers step by step, for example 5s, then 2s, then 1s, then remove the lines. Note that the delay timers restart when you reload or stop Postfix.

If problems appear

• Many deferrals from one provider: slow down for that provider (How to set delivery rate limits per provider in Postfix and handle deferrals?).
• Bounces with reputation or policy text: read the message, stop growing and follow What to do when your IP address is on a blocklist or your mail is rejected?.
• Complaints rise: check that recipients asked for the mail and that unsubscribing is easy.

Frequently asked questions

How long does warm-up take?
Some weeks for a normal volume; more for very large volumes. There is no shortcut.

Can I warm up several addresses at the same time?
Yes, but each with its own small volume of the mail it will really send. Do not split one stream over many addresses just to look bigger.

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