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· 7 min read

How to Warm Up a New Email Domain (The Right Way)

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New domain. New mailboxes. Exciting.

Now slow down — because if you start sending cold emails before the warmup is done, you’ll tank your domain reputation before a single prospect reads your message. And a burned domain is nearly impossible to recover.

Here’s exactly how to warm up a new sending domain, what shortcuts to skip, and when you’re actually ready to send.

Why warmup exists

Mail servers decide whether to deliver your email to the inbox or spam based on a sender reputation score. This score is built over time from signals like:

  • Volume patterns — how many emails you send per day, and how that changes
  • Engagement — are recipients opening, replying, and keeping your emails?
  • Bounce rate — are you sending to valid addresses?
  • Spam complaints — are people hitting “report spam”?

A brand new domain has zero history. ISPs don’t trust zero-history senders. Send 200 emails on day one and every major spam filter will flag you immediately.

Warmup is the process of building reputation gradually — teaching ISPs that your domain sends mail people want.

Step 1: Buy and configure your sending domain

Before warmup starts, your DNS has to be perfect.

Buy a secondary domain — never warm up your main company domain for cold email. Use a close variant like get[yourbrand].com, try[yourbrand].com, or [yourbrand]hq.com.

Then configure:

SPF record

v=spf1 include:_spf.google.com ~all

DKIM — generated through your email provider (Google Workspace, Microsoft 365). Add the provided TXT record to your DNS.

DMARC

v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com

MX records — set automatically when you connect the domain to Google Workspace or Microsoft 365.

Verify all of these before touching warmup. Use MXToolbox to check SPF, DKIM, and DMARC. All three must pass.

Also: set up a domain redirect. Your secondary domain should 301-redirect to your main website. It adds a small reputation signal and looks legitimate to anyone who types the domain into a browser.

Step 2: Set up your mailbox

For cold email, Google Workspace outperforms Microsoft 365 in most niches. Google has the largest share of business inboxes and its own reputation scoring is more forgiving for new senders.

Mailbox settings to configure

Display name: Use a real first name + last name. “Alex Chen” beats “BuyerBrains Sales” for reply rates and looks more human to spam filters.

Profile photo: Add one. It’s a trust signal.

Email signature: Keep it minimal — name, title, company, one link. No images, no banners.

Forwarding: Forward all incoming mail to your main inbox. You’ll get replies to cold emails and you need to see and respond to them.

Conversation history: Turn on “smart reply” and conversation threading in Gmail. You want every reply interaction treated as a thread.

Step 3: The warmup schedule

The warmup period is 6–8 weeks for a new domain. There are no shortcuts. Anyone selling you a “3-day warmup” is selling you a burned domain.

Weeks 1–2: Manual warmup only

Send 5–10 real emails per day to people in your network — colleagues, friends, past clients. Ask them to reply. These replies are the highest-quality engagement signal possible.

Do not use a warmup tool yet. Tools generate synthetic engagement; real engagement is far more valuable in the first two weeks.

What to send: anything that generates a reply. Ask for feedback on something. Share something relevant. It doesn’t matter — you’re building a sending pattern, not running a campaign.

Target: 80%+ reply rate. If the people you’re emailing aren’t replying, you’re emailing the wrong people.

Weeks 3–4: Add a warmup tool

At this point, layer in a warmup tool. Good options:

  • Instantly Warmup (free with Instantly account)
  • Lemwarm (standalone, works with any mailbox)
  • Mailreach (good reporting on placement)

Set the tool to send 20–30 warmup emails per day in addition to your manual sends. Total volume: 25–40 emails/day.

Warmup tools work by connecting your mailbox to a pool of other warmed mailboxes. They send each other emails, auto-open them, move them out of spam, and auto-reply. It’s synthetic, but the engagement pattern is consistent and measurable.

Monitor: Check your spam placement rate in the warmup tool dashboard. It should be under 5%.

Weeks 5–6: Ramp to send volume

Increase warmup tool sends to 40–60/day. Start sending small cold batches (10–20/day) to your actual target list — high-quality accounts you’re most confident about.

Watch your reply rates and bounce rates closely. A bounce rate over 3% is a red flag — either your list is dirty or something is wrong with your infrastructure.

Target metrics at this stage:

  • Spam placement rate: < 3%
  • Bounce rate: < 2%
  • Reply rate: > 15% on warmup emails

Weeks 7–8: Full send volume

If metrics are clean, ramp to full cold email volume: 50–80 emails/day per mailbox.

Keep warmup tool running in the background indefinitely. Most experienced operators leave warmup on even after the domain is established — it maintains a baseline of positive engagement signals.

Step 4: What to monitor during warmup

Google Postmaster Tools

Free, takes 5 minutes to set up, essential. Monitors your domain reputation from Google’s perspective on a scale: Bad → Low → Medium → High.

You want to stay at High. If you drop to Medium, slow down. If you drop to Low, stop cold sending immediately and diagnose the problem.

Also monitors spam complaint rate. Google recommends staying under 0.1%. Above 0.3% and you’ll start seeing systematic spam placement.

Warmup tool dashboard

Check daily during warmup, weekly after:

  • Inbox placement rate (target: > 95%)
  • Spam placement rate (target: < 3%)
  • Reply rate on warmup emails (target: > 80%)

Bounce rate in your sending tool

Monitor every campaign. Consistently over 3% means your list needs cleaning. Use a tool like NeverBounce or ZeroBounce to verify email addresses before sending.

Common warmup mistakes

Starting too fast

Volume spikes are the #1 cause of warmup failure. Going from 10 emails/day to 100 emails/day overnight triggers spam filters regardless of how good your DNS setup is.

The schedule above is a minimum. You can go slower. Never go faster.

Using warmup to replace real engagement

Warmup tools are useful but they produce synthetic engagement. They don’t replicate the signal of a real person reading your email and choosing to reply. The first two weeks of real sends matter more than the following four weeks of tooling.

Sending to a dirty list

If your cold email list has 20% invalid addresses, your bounce rate will immediately flag your domain. Clean your list before sending a single email.

Abandoning warmup after a few weeks

Warmup isn’t a phase — it’s infrastructure. Keep the tool running. Keep monitoring Postmaster Tools. The moment you stop paying attention is usually the moment something goes wrong.

Using the sending domain for marketing emails

Your sending domain should only send cold email. Marketing emails (newsletters, drip campaigns, transactional emails) go through your main domain or a dedicated marketing domain. Mixing them creates deliverability conflicts.

When are you actually ready to send at full volume?

You’re ready when all of the following are true for at least two consecutive weeks:

  • Google Postmaster domain reputation: High
  • Warmup tool spam placement rate: < 3%
  • Bounce rate on test sends: < 2%
  • You’ve been warming for at least 6 weeks
  • Your DNS (SPF, DKIM, DMARC) is fully verified

If any of these aren’t met, you’re not ready. Sending early will cost you the domain — and then you start over.

The infrastructure we set up for clients

At BuyerBrains, the first thing we do with any new client is set up their sending infrastructure properly:

  • Buy 2–3 secondary sending domains
  • Configure full DNS on all domains
  • Set up Google Workspace mailboxes (2 per domain)
  • Run 6-week warmup with a combination of manual and tool-based sends
  • Set up Google Postmaster monitoring before day one
  • Verify list quality before any cold sends begin

This takes about 6 weeks before the first campaign goes out. It feels slow. It is slow. But clients who skip this step and send early almost always come back after killing a domain, and then we do it properly anyway — just starting from zero.

Do it right the first time.