Warm up a new email domain for at least 14 days before you send a single cold email, then build cold volume slowly over another 14 days. Expect about 4 weeks from a brand-new domain to full sending volume.
This page explains how warm-up works, gives the exact schedule we use, and shows how to tell when a mailbox is ready. For where warm-up fits among domains, lists and copy, see our guide to cold email for agencies.
How long should you warm up an email domain before a cold email campaign?
Warm up for 14 days at minimum, and only start cold sending once the warm-up results are clean. Fourteen days is a floor, not a finish line: a mailbox whose warm-up mail still lands in spam on day 14 needs longer.
The full timeline from purchase to full volume looks like this:
| Stage | Days | Cold emails per mailbox per day |
|---|---|---|
| Buy domains, create mailboxes, set DNS | Day 0 | 0 |
| Warm-up only | Days 1 to 14 | 0 |
| Cold ramp, with warm-up still running | Days 15 to 28 | 5 rising to 30 |
| Full volume | Day 29 onward | 30 |
The cold ramp counts weekdays, so in calendar time the second stage runs closer to three weeks. Plan for a month before a new setup sends at full volume.
What is email warm-up for cold email?
Email warm-up is a period of small, normal-looking email traffic that gives a new mailbox a sending history before it sends cold email. It exists because inbox providers judge senders by their past behavior, and a new mailbox has none.
To Gmail or Outlook, a mailbox that appears from nowhere and sends 50 emails to strangers looks exactly like a spammer who just registered. A mailbox that has sent and received a growing number of opened, replied-to emails for two weeks looks like a person.
Warm-up does not make bad email good. It builds a starting reputation so that good email gets a fair chance at the inbox. Our step-by-step page shows how to warm up an email domain, including doing it by hand.
How does cold email warm-up work?
Warm-up tools connect your mailbox to a network of other real mailboxes that email each other automatically. Each day your mailbox sends a few messages to the network and receives a few back. Whether that actually helps is a fair question; our guide to whether email warm-up works weighs the evidence.
The network then behaves like interested readers:
- It opens your messages, which tells providers people want your mail.
- It replies to a share of them. Replies are the strongest positive signal a provider sees. We set warm-up replies at 45% of messages.
- It rescues your mail from spam. If a warm-up message lands in a spam folder, the recipient mailbox in the network moves that message to the inbox, which tells the provider the mail was wrongly filtered.
- It reports where each message landed. That gives you an inbox-versus-spam rate for your own mailbox, which is the number that tells you whether warm-up is working.
Volume grows a little each day. A mailbox that jumps from 0 to 50 emails a day looks compromised, even if every recipient is friendly.
What does a cold email warm-up schedule look like?
A good warm-up schedule starts with a handful of emails a day and adds a few more each day. This is the schedule Pipefire runs on every new mailbox:
| Warm-up day | Warm-up emails sent | Cold emails sent |
|---|---|---|
| 1 | 4 | 0 |
| 2 | 6 | 0 |
| 3 | 9 | 0 |
| 4 | 12 | 0 |
| 5 | 16 | 0 |
| 6 | 20 | 0 |
| 7 | 24 | 0 |
| 8 | 28 | 0 |
| 9 | 32 | 0 |
| 10 | 36 | 0 |
| 11 | 40 | 0 |
| 12 | 44 | 0 |
| 13 | 47 | 0 |
| 14 | 50 | 0 |
No cold email goes out in these 14 days. Once the mailbox passes its readiness check, cold volume ramps over the next 14 sending days while warm-up keeps running alongside:
| Cold sending day | Cold emails | Warm-up emails | Total |
|---|---|---|---|
| 1 | 5 | 50 | 55 |
| 4 | 10 | 50 | 60 |
| 7 | 16 | 50 | 66 |
| 10 | 22 | 50 | 72 |
| 14 | 30 | 50 | 80 |
The full cold ramp is 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 and 30. We cap each mailbox at 80 emails a day in total, warm-up included, and never above 30 cold.
Pipefire runs both schedules automatically on every mailbox; our built-in email warmup tool shows what you see while it happens.
How do you know warm-up is finished and cold email can start?
Warm-up is finished when the mailbox has served its 14 days and its warm-up mail is landing in the inbox, not the spam folder. Measure it, rather than trusting the calendar.
Our readiness rule is simple and strict:
- At least 14 days of warm-up. No exceptions for a mailbox that looks fine early.
- Fewer than 10% of warm-up emails in spam over the last 7 days.
- At least 20 warm-up emails measured in that window. A rate on a handful of emails is noise, so a mailbox without enough data waits.
A mailbox that misses the rule keeps warming and is checked again the next day. It does not get a cold email until it passes.
Can you skip warm-up or use pre-warmed mailboxes for cold email?
Do not skip warm-up on a new mailbox. Sending cold email on the first day is the fastest way to burn a new domain. A burned domain usually has to be replaced, which restarts the 4-week clock.
Pre-warmed mailboxes are a real option. Some providers sell mailboxes that have already been warming for weeks, so cold sending can start sooner. Two cautions apply:
- Check the warm-up results yourself before sending. "Pre-warmed" describes time spent, not results.
- Still ramp cold volume. A warm mailbox that jumps straight to 30 cold emails a day changes its pattern overnight. Our cold email mailboxes guide explains where the 30-a-day ceiling comes from.
Buying domains early is the cheapest way to avoid both problems. The warm-up clock starts the day the mailbox goes live, so domains bought a month before a campaign are ready when it starts. Our guide to cold email domains covers how many to buy and how to set them up.
Should warm-up keep running after you start sending cold email?
Yes. Keep warm-up running for as long as the mailbox sends cold email. It adds a steady stream of opened and replied-to mail alongside your outreach, which balances the lower engagement that cold email naturally gets.
It also keeps measuring. The warm-up spam rate is your early warning system: when it rises, cold email from that mailbox is probably slipping into spam too, often before replies visibly drop.
What if cold email warm-up is not working?
If warm-up mail keeps landing in spam after 14 days, the problem is usually the setup, not the warm-up. Check these in order:
- Authentication. SPF, DKIM and DMARC must all pass. A single missing record can send everything to spam.
- The domain name and extension. A domain on an extension spammers favor, or one that looks like a throwaway, starts with a handicap.
- The mail provider. Mailboxes on Google Workspace or Microsoft 365 start with the provider's own reputation behind them.
- The domain's past. A domain that was used for spam before you bought it can carry that history.
If the rate stays high after those checks, retire the domain and replace it. Apollo's own guidance warns that warm-up may not be enough to recover an already damaged reputation, and recommends starting fresh with a new domain or mailbox instead.
The same signal works in reverse for a mailbox already sending. If a sending mailbox's warm-up spam rate climbs past 20%, we take it off cold email and put it back into warm-up. It returns to cold at 5 a day once it lands in the inbox again. Our deliverability page explains the other automatic pauses, for bounces and complaints, and our cold email deliverability guide shows how to fix a domain that keeps slipping.
What should you look for in a cold email warm-up tool?
Look for a tool that reports where your warm-up mail lands, not just how much it sends. Without an inbox-versus-spam number, you cannot tell when a mailbox is ready. Our guide to choosing a cold email warm-up tool goes through what to look for and what each type costs.
| Feature | Why it matters |
|---|---|
| Inbox versus spam reporting | The only real test of whether warm-up is working |
| A gradual ramp you can see | A sudden jump looks like a hijacked account |
| Replies, not just opens | Replies are the strongest positive signal |
| Runs alongside cold sending | Warm-up should never stop while a mailbox sends |
| A large, real network | Many real mailboxes across providers, not a few test accounts |
Most cold email platforms include warm-up in their plans, so you rarely need a separate tool. What usually goes missing is the rule that holds a mailbox back until it is ready. That part is down to you, unless your platform enforces it.
Ask a platform how it enforces that rule before you rely on it. "We include warm-up" and "we will not let a mailbox send cold email until its warm-up results are clean" are different promises. Only the second one protects a new domain from a setup that looks ready but is not.
Cold email warm-up FAQ
Is 2 weeks of warm-up enough for cold email?
Two weeks is the minimum, not a finish line. Most mailboxes on a good domain and provider are ready after 14 days, but confirm it by checking the warm-up spam rate before you send.
Can I send cold emails while warming up?
No. Keep cold sending at zero until warm-up is finished and the results are clean, then start at about 5 a day.
How many warm-up emails should a cold email mailbox send per day?
Start with about 4 a day and build to about 50 by the end of the second week. Add 3 or 4 emails a day, not large jumps.
Do I need to warm up a cold email domain or each mailbox?
Each mailbox. Every mailbox builds its own sending history, and each one on a domain also adds to that domain's reputation.
Does cold email warm-up work for Microsoft 365 as well as Google Workspace?
Yes. Warm-up works the same way on both. Some Microsoft 365 setups need SMTP sending turned on before a warm-up tool can connect.
Should I turn warm-up off once a cold email campaign starts?
No. Keep it running for as long as the mailbox sends cold email, because it keeps measuring placement and keeps positive engagement flowing.