Email warm-up is the process of increasing your sending volume gradually on a new domain or IP address so mailbox providers learn that your mail is wanted. A brand-new sender has no history, and a sudden burst of thousands of messages looks exactly like spam. A careful warm-up, starting with your most engaged recipients and growing over about 30 days, is how you build a reputation that carries your campaigns to the inbox.
Before you start. Warm-up only works on top of correct authentication. Publish SPF, DKIM and DMARC first by following the sending domain authentication guide.
What is email warm-up and why does it matter?
Receiving servers decide where to place your mail using signals they have learned about you: complaint rates, bounce rates, engagement, spam traps and consistency. A new domain or IP address has none of these signals, so providers are cautious. They may defer or throttle your mail, send it to spam or reject it, until you show a track record of sending mail people want.
Warm-up is your way of creating that track record on purpose, at a pace the providers can trust. It protects three things:
- Inbox placement. Good early signals mean later campaigns start from a high baseline.
- Sender reputation. Reputation is much slower to rebuild than to build, so protecting it early is cheaper.
- Your IP and domain. A bad first week can land you on a blocklist that takes weeks to clear.
Domain warm-up vs IP warm-up
You may need to warm up an IP address, a domain, or both, depending on your setup. Large mailbox providers such as Gmail evaluate domain reputation heavily, while IP reputation is still important for many receivers.
| Situation | Warm up IP? | Warm up domain? | Notes |
|---|---|---|---|
| New domain on a shared IP | No | Yes | The IP already has traffic, but your domain has no history. |
| New domain on a new dedicated IP | Yes | Yes | The longest ramp. Plan four to eight weeks. |
| Existing domain, new dedicated IP | Yes | Usually no | Domain reputation transfers, but start slowly on the IP. |
| Existing domain moving providers | Depends | No | Keep the domain, ramp up the new infrastructure gradually. |
| Domain idle for months | Maybe | Yes | Treat it as partly cold and ramp up again. |
Before you send the first message
- Authenticate. SPF, DKIM and DMARC should all pass, aligned with your From domain.
- Set up monitoring. Register your domain with Google Postmaster Tools, enrol your IPs in Microsoft SNDS and the Junk Mail Reporting Program, and sign up for Yahoo's complaint feedback loop if available to you.
- Clean your list. Remove invalid addresses, role accounts such as info@ and admin@ where possible, and anyone who has not engaged in the last 6 to 12 months.
- Add working unsubscribe. Include a visible link and the List-Unsubscribe headers for one-click unsubscribe.
- Decide on streams. Keep transactional and marketing mail on separate subdomains.
Who to send to first
Warm-up is as much about who as how many. Positive engagement early teaches providers that your mail is wanted. Order your recipients like this:
| Priority | Segment | Why |
|---|---|---|
| 1 | Transactional mail (sign-up confirmations, receipts, password resets) | Recipients expect it and almost always open it. |
| 2 | Customers who purchased or logged in during the last 30 days | Highest likelihood of opens and clicks. |
| 3 | Subscribers who opened or clicked in the last 60 to 90 days | Known to be active. |
| 4 | Subscribers with older engagement (3 to 6 months) | Add only after earlier steps look healthy. |
| 5 | Never-engaged and long-inactive contacts | Add last, or run a re-confirmation campaign instead. |
Never use a purchased or scraped list. It produces spam traps, bounces and complaints within days and can undo weeks of warm-up. Send only to people who have agreed to hear from you.
A 30-day warm-up schedule
Use this as an illustrative starting plan for a new domain or dedicated IP aiming at around 50,000 messages a day. The right schedule depends on your target volume and on what you see. If you are sending smaller volumes, stop at the step that matches your regular daily volume.
| Days | Messages per day | Audience |
|---|---|---|
| 1 to 2 | 50 | Transactional and most engaged customers only |
| 3 to 4 | 100 | Same segment |
| 5 to 6 | 250 | Add recent buyers |
| 7 to 8 | 500 | Add 30-day openers and clickers |
| 9 to 10 | 1,000 | Same |
| 11 to 12 | 2,500 | Add 60-day engaged |
| 13 to 14 | 5,000 | Same |
| 15 to 18 | 10,000 | Add 90-day engaged |
| 19 to 22 | 20,000 | Same |
| 23 to 26 | 35,000 | Add older engaged subscribers |
| 27 to 30 | 50,000 | Full list of engaged recipients |
Each step is roughly a 50 to 100 percent increase. Do not move to the next step until the previous two days looked healthy. If anything on the monitoring list turns red, hold the volume or step back.
Spread sends through the day
Large providers prefer steady patterns. Instead of sending your whole daily volume in one burst, spread it over several hours or in batches. If your platform supports throttling, set a message-per-hour limit that matches your schedule.
What to monitor every day
| Signal | Healthy | Act when | Where to see it |
|---|---|---|---|
| Hard bounce rate | Under 2% | Over 2% for a day | Your delivery logs and reports |
| Spam complaint rate | Under 0.10% | Reaches 0.10% or more | Google Postmaster Tools, feedback loops |
| Deferrals (4xx) | Rare and short-lived | Repeated throttling messages | Delivery logs. See bounce codes explained |
| Domain and IP reputation | Medium to high | Drops to low or bad | Google Postmaster Tools, Microsoft SNDS |
| Opens and clicks | Stable or rising | Falling sharply | Your campaign reports |
| Blocklist listings | None | Any major listing | Spamhaus and other lookup tools |
| Inbox placement | Mostly inbox | Spam folder in test accounts | Seed test accounts at major providers |
A note on open rates. Apple Mail Privacy Protection preloads images, which inflates open counts for many recipients. Use clicks, replies and complaint rates as your main engagement signals during warm-up.
When to slow down or pause
- Hard bounces go above 2%. Stop increasing volume. Check for typos, old addresses or an import problem and suppress the bad addresses.
- Complaints reach 0.10%. Pause increases, tighten your audience to the most engaged recipients and review how people subscribed.
- Providers defer or throttle you. Reduce your sending rate, keep retrying as your system normally would and resume increases only when deferrals stop.
- Domain reputation drops. Return to the last volume that held a healthy reputation and stay there for several days.
- You hit a blocklist. Stop sending, find the cause, fix it and follow the blocklist operator's removal process.
Stepping back is not failure. A short pause costs days; a damaged reputation costs weeks.
Shared vs dedicated IP: which should you use?
| Shared IP | Dedicated IP | |
|---|---|---|
| Warm-up | Provider manages most of it | You must warm it up yourself |
| Reputation | Shared with other senders, managed by the provider | Entirely yours, good or bad |
| Best for | Lower or variable volume, getting started quickly | Steady high volume and a need for full control |
| Risk | Another sender can affect the pool | Low volume can leave the IP "cold" |
| Rule of thumb | Under a few hundred thousand messages a month | Consistent, high daily volume |
A dedicated IP is not automatically better. If your volume is low or sporadic, a well-managed shared IP often delivers better results because the pool keeps its reputation warm.
Common warm-up mistakes
- Sending the entire list on day one.
- Skipping authentication, or using a platform default Return-Path and DKIM domain that does not align with your From address.
- Increasing volume on a fixed schedule even when bounces or complaints are rising.
- Mixing marketing and transactional mail on the same domain during warm-up.
- Warming only on weekdays and then sending heavy volume on weekends.
- Using cold, purchased or very old lists to hit volume goals.
- Ignoring the warm-up after day 30. Keep volume steady and avoid sudden jumps afterwards.
Warm-up checklist
- SPF, DKIM and DMARC pass and align.
- Postmaster Tools, SNDS and feedback loops are configured.
- List cleaned and segmented by engagement.
- One-click unsubscribe headers and a visible unsubscribe link in marketing mail.
- Day 1 volume set to about 50 messages, with a written step-up plan.
- Daily review of bounces, complaints and reputation dashboards.
- Clear pause rules agreed before you begin.
Planning a first campaign? Verify your domain, check your records and send your first messages from MigoSMTP.
Further reading and sources
Frequently asked questions
What is email warm-up?
Email warm-up is the gradual increase of sending volume from a new domain or IP address so mailbox providers can learn that your mail is wanted. You begin with a small number of messages to your most engaged recipients and increase over several weeks while monitoring bounces and complaints.
How long does it take to warm up a domain or IP?
A typical warm-up takes four to eight weeks to reach high volumes, and about 30 days for moderate volumes. The exact time depends on your target volume, list quality and how recipients react. Do not follow the calendar blindly: follow the signals.
How many emails should I send on day one?
Start with about 50 messages to your most engaged recipients, and keep the first week under a few hundred. Small early volume gives mailbox providers time to see positive engagement before the volume grows.
Do I need to warm up a shared IP?
Usually not, because shared IP addresses already carry traffic and reputation managed by the provider. You still need to warm up a new sending domain, and you should increase your own volume gradually even on shared IPs.
Do I need to warm up a new domain if my IP is already warm?
Yes. Gmail and other large providers weigh domain reputation heavily, so a new domain starts without history even on a well-known IP. Follow the same gradual schedule for the domain.
Can I warm up with a tool that sends fake engagement?
It is not a good idea. Automated peer-to-peer warm-up networks cannot replace real recipients, and providers can treat artificial engagement as manipulation. The reliable method is real mail to real, consenting recipients, ramped gradually.
What bounce and complaint rates are safe during warm-up?
Aim for hard bounces under 2 percent and spam complaints under 0.10 percent, which is the level Google recommends staying below. If you see a sustained rise in either, pause increases and fix the cause before sending more.
What if I stop sending for a few weeks?
Reputation fades when a sender goes quiet. After a long gap, return to a lower volume and ramp back up in steps instead of resuming at the old level.
Should I warm up transactional and marketing mail together?
Warm them up separately. Start transactional mail first, because password resets and receipts get high engagement, and keep marketing on its own subdomain so a complaint problem there cannot affect critical messages.
What should I do if my emails go to spam during warm-up?
Stop increasing volume, return to the last volume that reached the inbox, check authentication, remove unengaged recipients and review your content. Resume increases slowly once placement recovers.