Email warm-up: how to warm up a new domain or mailbox without landing in spam
What email warm-up is, an example ramp schedule for a new domain or mailbox, how marketing and cold email warm-up differ, and the signals that mean pause.
A new domain or mailbox has no sending history. To Gmail, Yahoo and Outlook, a sender with no history that suddenly sends thousands of emails looks a lot like a spammer or a hacked account. Email warm-up is the process of building a track record gradually, so mailbox providers learn that your mail is wanted before you send at full volume.
This guide covers when you need to warm up, an example schedule for a new domain and a new mailbox, how warm-up differs between marketing email and cold email, and the signals that tell you to slow down.
What email warm-up is
Mailbox providers judge mail largely on the reputation of the sender: the domain, the IP address and, for cold outreach, the individual mailbox. Reputation comes from history. How many messages were sent, how many bounced, how many people marked them as spam, how many were opened, replied to or moved out of the spam folder.
A brand-new sender has none of that. Warm-up means starting with a small daily volume to recipients most likely to engage, then increasing step by step while you watch the results.
Google's sender guidelines put it plainly: increase sending volume slowly, send at a consistent rate rather than in bursts, and if you start seeing bounces or deferrals, cut volume until errors drop, then increase slowly again.
When you need to warm up
- A new sending domain, including a new subdomain such as
news.example.com. - A new mailbox for cold outreach, even on an established domain.
- A new dedicated IP address. If you send through an email service's shared IPs, the IP already has history, but your domain still doesn't.
- A domain that has been quiet for months, or one that is jumping to a much bigger list (for example, from 2,000 to 50,000 contacts for a seasonal sale).
- Moving to a new email platform, where your mail now comes from different servers and possibly a new sending subdomain.
Before you send a single warm-up email, make sure SPF, DKIM and DMARC are in place and aligned. Warm-up builds reputation; authentication is what lets providers attach that reputation to your domain. Our SPF, DKIM and DMARC guide shows example records.
How to warm up a new email domain
Here is an example schedule for a new marketing domain sending to an opted-in list. It is a reasonable starting point, not a rule published by any mailbox provider. Adjust it to your list size and to the signals described below.
| Days | Daily volume (example) | Who to send to |
|---|---|---|
| 1–3 | 200–500 | Most engaged: opened or clicked in the last 30 days |
| 4–7 | 1,000–2,000 | Engaged in the last 60 days |
| 8–14 | 3,000–8,000 | Engaged in the last 90 days, plus recent sign-ups |
| 15–21 | 10,000–20,000 | Add 90–180 day engagers in batches |
| 22–30 | Full list | Everyone still consenting, older contacts last |
A few rules make the schedule work:
- Only increase when the last step was clean. No jump in bounces, deferrals or complaints.
- Avoid doubling overnight. Google warns that sudden spikes, especially without a history of large volumes, can trigger rate limiting or hurt reputation.
- Send at a steady rhythm. Spread sends across the day or the week rather than firing the whole list at 9:00.
- Send your best content first. A welcome series or a genuinely useful update earns opens and replies. A heavy discount blast to cold contacts earns complaints.
- Clean the list before you start. Remove hard bounces, role addresses you never collected and anyone who hasn't engaged in a long time. Old addresses are where spam traps and bounces hide; see email list cleaning.
How to warm up a new mailbox for cold email
Cold email is a different game. You are writing to people who didn't ask to hear from you, from individual mailboxes on Google Workspace, Microsoft 365 or similar. Volumes per mailbox are small and should stay small.
The shape of a ramp for one new cold outreach mailbox:
| Stage | Daily volume | Notes |
|---|---|---|
| First week | A small number a day | Normal one-to-one mail too, if the mailbox is used by a person |
| Following weeks | A small step up each week | Only if bounces stayed low the week before |
| Warmed up | A safe daily limit for one mailbox | Stays well below anything that looks like bulk sending |
Need more volume? Add mailboxes, ideally across a couple of domains, rather than pushing one mailbox past a safe daily limit. Spreading the same daily total across several mailboxes is safer than sending it all from one.
Other cold-specific rules:
- Use a separate domain, for example
getexample.comnext toexample.com, so outreach can never drag down the domain your receipts and newsletters use. - Verify addresses before sending. Bounces hurt a new mailbox fastest.
- Send in business hours, with random gaps between messages.
- Keep the first email plain: short text, no attachments, at most one link.
Our cold email deliverability guide covers the rest of the setup.
Marketing vs cold email warm-up
| Marketing email | Cold email | |
|---|---|---|
| What you warm | Domain (and IP if dedicated) | Each mailbox, plus its domain |
| Recipients | People who opted in | Prospects who didn't ask |
| Ramp | Hundreds to tens of thousands a day over weeks | A small number a day per mailbox, up to a safe daily limit |
| Scaling | Send to more of the list | Add more mailboxes |
| Main risk | Complaints from stale contacts | Bounces and spam reports from strangers |
| Unsubscribe | One-click unsubscribe required for bulk senders | An easy way to opt out in every email |
The biggest difference is the ceiling. A warmed-up marketing domain can send to its whole list. A warmed-up cold mailbox still sends only a modest number of emails a day; warm-up doesn't turn a single mailbox into a bulk sender.
What about automated warm-up tools?
Many cold email tools offer "warm-up networks": your mailbox exchanges messages with other mailboxes in the network, which automatically open them, reply and pull them out of spam. They can add activity to a brand-new mailbox, but the engagement is artificial, and it is not the same as real recipients wanting your mail. Treat them as a supplement at most. The reputation that matters is built by sending relevant mail to real people at a sensible pace.
Signals to watch during warm-up
| Signal | Where to see it | What it suggests |
|---|---|---|
| Hard bounce rate | Your sending platform | Bad or old addresses; clean the list |
| Deferrals (4xx errors) | Platform logs, bounce messages | The provider is rate limiting you; slow down |
| Spam complaint rate | Google Postmaster Tools, feedback loops | Recipients don't want this mail |
| Gmail compliance status | Google Postmaster Tools | Whether you meet Gmail's sender requirements |
| Outlook filter result | Microsoft SNDS (if you control the IP) | Share of your mail filtered as spam |
| Replies (cold) | Your inbox | The best sign that mail lands and is welcome |
| Opens and clicks | Your platform | A rough trend only; privacy features distort opens |
Google requires senders to keep the spam rate shown in Postmaster Tools below 0.3% and recommends staying under 0.1%. Yahoo also sets 0.3%. During warm-up, aim well under 0.1%.
When to pause
Pause, or step back to the previous day's volume, if you see:
- A jump in bounces. Find the source (an old segment, a bad import) before sending more.
- Deferrals or blocks from one provider, such as Gmail returning 421 or 550 errors. Hold volume to that provider until errors drop, as Google advises, then resume slowly.
- Spam rate climbing towards 0.1% in Postmaster Tools, or any complaint spike.
- Postmaster Tools showing a compliance problem.
- For cold email, replies stopping completely while sends continue. That often means mail is landing in spam.
After a pause, restart below the level where problems began and climb more slowly. Fix the cause first; ramping again with the same list or content gives the same result.
How EterMail ramps cold mailboxes
EterMail is our product. For cold outreach, you connect your own Google Workspace, Microsoft 365 or SMTP mailboxes on a separate domain. Each new mailbox starts with a small number of emails a day, steps up each week and stops at a safe daily limit; you can adjust the ramp per mailbox. If a mailbox's bounce rate reaches 2%, its ramp holds and that day's limit is halved; at 3% it pauses and you're told why. Sends spread across business hours with gaps between them, and a sequence stops as soon as the prospect replies.
For marketing email, a new workspace's sending also ramps up over its first week; emails above the day's limit wait in the queue instead of being dropped. EterMail also sends at most one marketing email per contact per 24 hours. Warm-up is one part of deliverability; the email deliverability guide covers the rest.
FAQ
How long does it take to warm up an email domain?
For a marketing domain, plan on two to four weeks before sending to your whole list, longer for very large lists. A cold outreach mailbox usually takes a few weeks to reach its daily ceiling. The pace depends on your results: only increase volume when bounces, deferrals and complaints stay low.
How many emails should I send when warming up?
There is no official number; mailbox providers only say to increase slowly and steadily. As an example, a marketing domain might start with a few hundred emails a day to its most engaged subscribers, and a cold mailbox with a small handful a day. Increase in steps rather than doubling overnight.
Do I need to warm up a new domain if I use an email service provider?
Yes. On a provider's shared IPs, the IP already has history, but your domain doesn't, and mailbox providers track domain reputation too. Send to your most engaged contacts first and build up over a few weeks.
Do email warm-up tools work?
Warm-up networks create artificial opens and replies between participating mailboxes. They can add early activity to a new mailbox, but they can't replace genuine engagement from real recipients. Authentication, clean lists, steady volume and relevant content matter more.
Can I warm up a domain that already has a bad reputation?
You can rebuild it, but slowly. Fix the cause first: remove unengaged and invalid addresses, check authentication and stop whatever drove complaints. Then restart at low volume to your most engaged contacts and increase gradually while watching Postmaster Tools.
Should I warm up a subdomain separately?
Yes, treat a new sending subdomain as a new sender and ramp it up. Google counts all mail from the same primary domain when deciding who is a bulk sender, so a subdomain doesn't hide volume, but its reputation still starts from little or no history.