Domain Warmup: How Long It Takes and How to Set It Up

Why shouldn't you send cold email from your main domain?

Because a domain's reputation is shared by everything sent from it, and cold outreach is the riskiest thing you can put on it.

Gmail and Outlook count everything from the domain in one pot: volume, bounces, spam reports. Weeks of bad cold outreach drag all company mail down, and nothing rolls that back.

The best argument for the main domain is trust, since recipients know it from your website. True, but I think the gap is small when the secondary domain carries the brand, redirects to the main site and is signed by a real person. A mistake the other way costs far more.

What is a secondary domain and how do you choose one?

A secondary domain is an extra domain bought only for outbound, with a name close to your brand, so recipients know who is writing and your main domain stays safe.

Common choices add a short prefix or suffix (like get, try or hq), or keep the name on another ending, like .co or .io. I'd avoid hyphens, numbers and long names that look like imitations.

A domain registered yesterday, with no website, that suddenly sends email is exactly what filters hunt for. Redirecting it to your main site makes it look like a real business from day one.

How do you set up domains and inboxes on Google Workspace and Outlook?

Buy the domain from a registrar, open inboxes on it in Google Workspace or Microsoft 365, and set the DNS records that connect the two.

Every LeadBound cold email setup includes 100 warmed inboxes, on Outlook and Google Workspace, on dedicated secondary domains. Why both? Recipients split between them, and each behaves differently.

Know the official limits, so they don't mislead you:

As of 2026 both are system ceilings, and Microsoft's document even says Exchange Online isn't meant for bulk mail. A cold inbox survives at far lower volume.

Which DNS records do you need before you start?

Four: MX to receive replies, SPF to approve who sends, DKIM to sign messages, and DMARC to decide what happens when a check fails. Each is explained in why emails go to spam.

From an empty domain to an inbox ready for warmup:

1. Buy a secondary domain close to your brand name.
2. Redirect it to your main website.
3. Open inboxes under real people's names.
4. Set MX, SPF and DKIM per the provider's instructions.
5. Publish DMARC. Start at p=none and tighten later.
6. Send a test email to Gmail and check that Show original reads PASS for every check.
7. Turn on warmup, and keep the inbox out of campaigns until it ends.

Step 6 sounds unnecessary until records shown in a provider's dashboard turn out never to have reached DNS. Only what the world sees counts.

What is email warmup, and how long does it take?

Email warmup is a period when a new inbox trades emails with a network of other inboxes that open them, reply and pull them out of spam, so providers see normal behavior. Ours lasts 14 days, with a gradual volume ramp.

Smartlead's data, based on more than 850 million emails sent through its platform from January to June 2026, puts the average sender at 8 days of warmup. I think that's too short. Even after 14 days, the results decide: a rising warmup score, emails that stay out of spam, and replies.

Warmup builds history for one inbox. Domain age builds for the whole domain, and you can't speed it up, so a domain registered this month starts with less trust even after a full warmup.

Warmup also stays on for the inbox's whole life. When something looks wrong, cut cold sending and keep the warmup. In Israel that includes the fall holidays: if a campaign pauses until after Sukkot, warmup keeps running and cold volume returns gradually.

What does a sample warmup schedule look like?

A good schedule starts at zero cold emails and adds volume only after each stage stays clean. This sample for one inbox is illustrative, and it stays within the 15 a day or fewer that Hunter recommends for beginners:

The calendar alone never justifies a step up. If bounce jumped in week 4, stay at week 3 another week.

How many inboxes per domain, and how many emails per inbox a day?

There's no official number, but common advice converges on two to five inboxes per domain and at most about 50 cold emails a day per warmed inbox.

Hunter's cold email guide, from December 2023, says fewer than five inboxes per domain works best, and some recommend two. Hunter calls 50 a day usually safe for a warmed inbox and suggests beginners start at 15 or fewer. Smartlead's 2026 data describes a common guideline of two or three inboxes per domain, a median of 14 cold emails a day per inbox, and 50 as a ceiling.

I lean toward the low end and add inboxes and domains for volume. A sample calculation: 300 cold emails a day at 15 per inbox is 20 inboxes, and at three per domain that's 7 domains, plus a few in reserve. The high-volume campaign playbook shows this in a real campaign, and what outbound costs in Israel prices it.

How do you monitor infrastructure and keep bounce under 2%?

Track a few numbers weekly, and verify every address before a campaign. Our bounce stays under 2% mainly because of that verification.

• Bounce, per campaign and per inbox.
• Inbox placement, using test inboxes at Gmail and Outlook.
• Reply rate over time. A drop on the same list and copy is an early warning.
• Blocklists such as Spamhaus and SURBL.
• Warmup that actually runs. A toggle in the dashboard doesn't prove emails went out.

Small numbers mislead: one bounce in twenty emails is 5%, and still one email.

When is a domain burned, and what do you do?

A domain is burned when it lands in spam at most providers even though authentication passes, volume is low and the list is clean, so the problem sits in its reputation.

The signs: rejection errors, blocklist listings, placement tests in spam everywhere, and fewer replies with no change to list or copy.

Before replacing it, see where the problem clusters. Bounces on one copy variant are a copy problem. On one inbox, it's the inbox. On one recipient provider, probably a security gateway on their side. Spread out and high, it's the list. A truly burned domain leaves the campaigns, and its volume moves to healthy domains and a reserve that's already warm. A domain bought mid-crisis needs a full warmup first, so warm reserves in advance.

LinkedIn has none of this. We run it from the client's existing profile, with no new account and no warmup, so it can start while email warms up. More on LinkedIn outreach.