How long to warm up a new inbox before cold email
By Travis Heurtelou · 5 min read · October 10, 2026
The short version
- Plan on four weeks of warm-up before a new inbox sends cold at full volume.
- Week one looks bad on almost every warm-up dashboard. Judge an inbox against inboxes of the same age, not against zero.
- Warm-up never stops. It keeps running alongside the cold sends.
- Check DNS, blacklists and bounce rate before the first cold email. Warm-up can't fix a broken setup.
What warm-up does
A new domain has no history. Gmail and Outlook don't know whether it's a person or a spammer, so the first emails it sends get treated with suspicion. Warm-up tools send emails between a network of real inboxes, open them, reply to some, and pull them out of spam when they land there. Over a few weeks the domain builds a record of people opening and answering its mail.
The timeline we use
| Week | Warm-up | Cold sends |
|---|---|---|
| 1 | Running, low daily volume that climbs | None |
| 2 | Running | None |
| 3 | Running | None, or a small test if the numbers have settled |
| 4 onward | Keeps running, every day | Full volume, about a dozen per inbox per day |
Why week one looks bad
Warm-up dashboards show what share of the warm-up emails landed in spam. On a brand-new domain that number is often high in the first week. In our own fleets it has read around a third in week one and fallen toward zero by week four, on the same vendor and the same setup.
So the useful comparison is an inbox against other inboxes of the same age. A week-one inbox at 30% is normal. A week-four inbox still at 30% has a problem: check its DNS records and whether the domain picked up a blacklist entry.
The dashboard number is also a lagging one. Most tools report a rolling window, so the early bad days stay in the figure for a week after things improve.
Warm-up keeps running
Turning warm-up off once cold sending starts is a common mistake. The warm-up traffic is what keeps the share of opened, answered mail high while the cold emails go out. Keep the warm-up volume above the cold volume on every inbox.
Before the first cold send
- SPF, DKIM and DMARC records are set and passing on the domain.
- The domain isn't on a public blacklist.
- The list has been verified, so the bounce rate starts near zero.
- The tracking domain is set up, or tracking is off.
Four weeks of warm-up, then cold. Compare inboxes to others the same age. Keep warm-up running for the life of the inbox.
Questions
Can I buy pre-warmed inboxes?
Yes, several vendors sell inboxes that have already been warming for weeks. That saves the wait, but check the domains yourself before you send.
Does warm-up guarantee the inbox?
No. It builds history. A bad list or a spammy email will still land in spam on a well-warmed domain.
What if an inbox is still landing in spam after a month?
Take it out of rotation, check the DNS records and blacklists, and keep it warming. If it doesn't recover, retire the domain.
Related
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