Email warm-up: how to warm up a new domain or IP address

A brand-new domain or IP address has no sending history, and receivers treat the unknown with caution. Warming up is how you build that history on purpose: you send a small amount of mail that people want, then increase it gradually while watching how receivers respond. This guide explains why it matters, a cautious way to ramp, and the signals that tell you to speed up or slow down.

Why do new domains and IPs need warming up?

Mailbox providers judge mail partly on the past behavior of the domain and IP that sent it. With no past, they have nothing to go on.

The M3AAWG Sender Best Common Practices put it plainly: the reputation of a newly registered domain "usually starts as unknown, which makes it similar to bad in that it does not yet have any sending history." With no history, filters treat incoming messages "with more scrutiny and caution."

IP addresses work the same way. Microsoft's guidance for senders says IP addresses that have never sent email "typically don't have any reputation in our systems," so mail from new sources is "more likely to experience delivery issues." Amazon SES says email providers "are less likely to accept mail from new IP addresses that have little or no history."

The risk is volume without history. Google's sender guidelines say to "avoid introducing sudden volume spikes if you do not have a history of sending large volumes."

When do you need to warm up?

Most small businesses only need to think about warm-up when they launch a newsletter, move to a new sending platform, or start sending from a new domain.

How long does warm-up take?

There's no fixed answer, and no major mailbox provider publishes a schedule. What the published guidance says:

• M3AAWG: "Consider 6 weeks of warm-up as an average."
• Amazon SES: For some providers, a new dedicated IP can establish a positive reputation "in around two weeks, while for others it may take up to six weeks." SES's own automatic warm-up for standard dedicated IPs runs over 45 days.
• Microsoft: A new IP "can expect to be fully ramped within a couple of weeks or less depending on volume, list accuracy, and junk email complaint rates."

Treat those as ranges, not deadlines. Your warm-up is done when you reach your normal volume without deferrals, rising bounces or complaints, not when a calendar says so.

What does a cautious warm-up plan look like?

The plan below is a general practice built from the guidance above. It deliberately has no daily numbers, because the right numbers depend on your list size, your audience and each receiver. If your email service provider offers automated warm-up, use it. SendGrid's automated warmup raises the volume on a new dedicated IP and sends overflow through another warm IP, and Mailgun says its queuing algorithms "gradually warm up your IPs."

Before you send anything

1. Authenticate everything. Publish SPF, set up DKIM for the new domain or subdomain, and publish DMARC. Check them with the SPF Checker, DKIM Checker and DMARC Checker.
2. Set up reverse DNS if you control the IP. Google requires valid forward and reverse DNS. Check it with the PTR Lookup.
3. Check blocklists. A "new" IP may have a past. Run it through the Blacklist Checker.
4. Register for monitoring: Google Postmaster Tools for the domain, and SNDS if you control the IP.
5. Send a test to the Email Deliverability Test and fix anything that fails.

The ramp

Three rules from the guidance apply at every phase:

• Start low and go slow. Google says to "start with a low sending volume to engaged users, and slowly increase the volume over time." Amazon SES says to send to "your most active users to ensure that your complaint rate remains low."
• Spread the mail out. M3AAWG says, "Do not send your daily batch all at once." Yahoo's FAQ also advises spreading a campaign out over time.
• Send regularly. M3AAWG says it's preferable to send campaigns on a regular basis until the domain is warmed up.

What about an existing domain on a new IP?

If your domain already has a good reputation, warm-up is often quicker. Microsoft says new IPs for domains with existing SPF records "typically experience the added benefit of inheriting some of the domain's sending reputation." That's not a reason to skip the ramp, only a reason it may go faster.

What should you watch during warm-up?

M3AAWG lists the signals to monitor, and the providers add their own tools.

1. SMTP logs. Check for deferrals and bounces every day. A temporary rejection such as Gmail's 421 4.7.28 means you're sending faster than Gmail wants from a new source. Microsoft may answer with 451 4.7.500-699 while it evaluates a source. Yahoo uses 421 TS deferrals.
2. Hard bounces. A burst of 550 5.1.1 "user unknown" replies points to an old or unconfirmed list. Stop and clean it before you continue. Our guide to hard and soft bounces explains what to remove.
3. Complaints and unsubscribes. Watch for spikes. In Postmaster Tools, keep the spam rate under 0.1%; see spam complaint rates explained.
4. Opens and clicks. M3AAWG notes that a sudden drop may mean your mail is going to junk, while large spikes may indicate security systems scanning your mail.
5. Postmaster Tools. Watch the spam rate and compliance status. Don't rely on the Domain and IP Reputation dashboards: Google says they will be retired and replaced with a new version.

When should you slow down?

Google's rule is direct: "If messages start bouncing or start being deferred, reduce the sending volume until the SMTP error rate decreases." Hold or step back when you see:

• Deferrals that persist for hours at one provider.
• Hard bounces above what your list normally produces.
• A rise in complaints or the Postmaster Tools spam rate.
• A new blocklist listing for your IP or domain.

Slow down only at the affected provider if your platform allows it. M3AAWG says you may need to slow sending "to some or all domains" when deferrals spike.

What should you avoid?

• Blasting your whole list on day one. This is the spike every provider warns about.
• Starting with your oldest contacts. Old addresses bounce and complain. Begin with the people most likely to welcome your mail.
• Artificial engagement. M3AAWG says "artificial warming practices are not recommended and may be illegal." Services that trade fake opens and replies between seed mailboxes don't build the reputation that matters.
• Mixing streams on a new IP. Yahoo says not to send bulk or marketing mail from the IPs you use for user and transactional mail. Warm each stream separately. Our guide to shared vs dedicated IPs covers how to split them.
• Going quiet afterward. Amazon SES advises keeping steady volume after warm-up and avoiding large sudden increases even once it's complete.

Next steps

1. Authenticate the new domain or subdomain and confirm SPF, DKIM and DMARC pass in a real message with the Email Deliverability Test.
2. Check the IP's reverse DNS and blocklist status before the first send.
3. Segment your list by recent engagement and start with the top segment.
4. Review SMTP logs and Postmaster Tools daily, and slow down at the first deferral spike.
5. If mail lands in spam during the ramp, work through why your emails are going to spam.

Browse more guides on running email day to day.