How to Warm Up a New Email Domain for Cold Email

A brand-new domain is a stranger to Gmail and Outlook. It has no sending history, so inbox providers have nothing to judge it by, and a sudden burst of email from an unknown domain looks a lot like spam. Warming up means building that history gradually, so that by the time you send at your real volume, the domain has a record of normal, wanted email.

Google says this directly in its sender guidelines: start with a low sending volume to engaged recipients, increase it slowly, send at a consistent rate rather than in bursts, and avoid sudden spikes. Everything below follows from that.

Before you send a single email

Warming up a domain that isn't set up properly wastes weeks. Get these right first.

1. Use a separate domain for cold outreach

Most teams send cold email from a domain that's close to their main one, such as getyourcompany.com or yourcompany.co, rather than the main domain itself. If a campaign draws complaints, the damage stays on the sending domain, not the one your invoices, proposals and client replies depend on.

Pick names that are obviously yours. A random-looking domain with no connection to your brand gets less trust from recipients, not more.

2. Make the domain look like a real business

• Redirect the website to your main site, so anyone who checks the domain lands somewhere real.
• Set up MX records so the domain can receive replies. A sending domain that can't receive mail is a red flag, and you'll lose replies.
• Create real-looking inboxes with a person's name, a profile photo and a simple signature.

3. Authenticate everything

Before the first send, the domain needs:

• SPF that includes your email provider and any sending tool, with one record and under 10 DNS lookups.
• DKIM switched on and signing as your domain, in your email provider and your sending tool.
• DMARC, starting at p=none with a reporting address.

Google requires SPF or DKIM from every sender, and SPF, DKIM, DMARC and alignment from anyone sending more than 5,000 messages a day to Gmail. Yahoo has the same rules for bulk senders. Our post on SPF vs DKIM vs DMARC explains each record, and the free email health check confirms they're live.

4. Decide on tracking

Open and click tracking add tracking links and pixels to every message. If you use them, set up a custom tracking domain on your own domain, so you aren't sharing reputation with every other customer of your sending tool. Many teams leave open tracking off entirely for cold email: it adds a tracking pixel to every message, and Google notes that open rates aren't a reliable signal of deliverability anyway.

5. Register with Google Postmaster Tools

Verify the domain in Google Postmaster Tools. Once you send enough volume to Gmail, it shows your spam rate and authentication results, which is the closest thing to a direct reading of how Gmail sees you.

The ramp: increase volume gradually

There is no official schedule. Google, Yahoo and Microsoft don't publish warmup numbers, and anyone quoting an exact "safe" figure is guessing. What they do publish is the principle: start low, grow slowly, stay consistent, and back off when you see errors.

Here's a conservative starting plan we use per inbox, to adjust based on what you see:

A few principles matter more than the exact numbers:

• Ramp per inbox and per domain. Volume is judged at both levels. Adding inboxes to one domain doesn't make the domain's growth any less sudden.
• Spread volume across inboxes rather than pushing one inbox hard.
• Send at a steady pace through the day, in business hours, not all at once.
• Start with your best-fit recipients. Early sends set the tone, and people who are likely to reply help your reputation.
• When errors appear, slow down. Google's guidance is to reduce volume if messages start bouncing or getting deferred, then increase slowly again.

What about automated warmup tools?

Many sending tools include "warmup": a network of inboxes that automatically email each other, open messages and move them out of spam. They're widely used, but be realistic about them. Inbox providers don't publish anything endorsing them, and they don't replace a clean setup and a gradual ramp of real, relevant email. If you use one, treat it as a supplement, keep it running at low volume alongside real sends, and don't read its "health score" as proof that your real emails reach the inbox.

Know your provider's limits

Each provider caps how much one account can send, and those caps are well above what a cold inbox should send:

• Google Workspace: 2,000 messages a day per user, with lower limits for trial accounts, plus caps on recipients per day. Hitting a limit blocks sending for up to 24 hours.
• Microsoft 365 (Exchange Online): a per-mailbox recipient rate limit over 24 hours, and a tenant-wide limit on external recipients that depends on how many licenses you have.

These are ceilings, not targets. A cold email inbox should run far below them. Both Google and Microsoft also prohibit spam in their terms, and accounts that send it can be suspended.

Signs the domain is ready, or in trouble

Ready:

• SPF, DKIM and DMARC all pass in the message headers (in Gmail, open a message and choose "Show original").
• Test messages to your own Gmail and Outlook.com addresses land in the inbox.
• Bounces are rare and complaints are near zero.
• Real recipients are replying, including the "not interested" ones.

In trouble:

• Gmail rate-limit or block errors such as 421 4.7.28 (unusual rate of email) or 550 5.7.26 (unauthenticated). See our 550 5.7.26 guide.
• Test messages start landing in spam.
• A spam rate in Postmaster Tools climbing toward 0.3%. Google asks senders to stay below 0.1%.

If you see trouble, cut volume, fix the cause, and ramp again slowly. Pushing through rarely works.

Keep it healthy after warmup

Warmup isn't a one-time event. Reputation is built continuously from how recipients react. Keep daily caps steady, clean bounces from your lists, honor opt-outs quickly (Yahoo asks bulk senders to honor unsubscribes within 2 days, and US CAN-SPAM rules require it within 10 business days), and rotate in fresh domains before the existing ones are worn out, not after.

Want it done for you?

Our Setup Sprint sets up up to 3 sending domains and 9 inboxes, with SPF, DKIM and DMARC on every domain, inboxes connected to your sending tool with warmup switched on, daily caps and a written 4-week ramp schedule. If you'd rather not run inboxes yourself, see how Google Workspace, Outlook and managed inboxes compare.