What warming up means
A brand new sending domain or address has no history. Mailbox providers such as Gmail and Outlook generally treat unknown senders with caution, because spammers often use fresh domains and send in large bursts. Warming up is the practice of starting with small volumes to the people most likely to welcome your mail, then increasing gradually so that a positive record builds up.
Providers do not publish exact thresholds, and no schedule is guaranteed to work. The approach below reflects widely used practice, and you should adjust it to what your own results show.
When you need to warm up
- You have registered a new domain for email.
- You are switching to a new email service that gives you a new sending address or a new IP address.
- You are starting email for the first time from a long-dormant domain.
- You are about to send far more than usual, for example to a list that has been silent for a long time.
Many email services share sending infrastructure across customers, in which case some of the groundwork has been done for you. Check your service’s current documentation for its recommendations; some provide their own warm-up guidance.
Do the technical setup first
Warm-up is wasted if the basics are missing. Before sending, make sure the domain has working email authentication (SPF, DKIM and a DMARC record), that the sender name and reply address are real and monitored, and that your email service has verified the domain. Send a test to a few personal inboxes at different providers, and check where it lands.
Start with your best contacts
Your first sends should go to people who have recently asked to hear from you and are likely to open and click: new subscribers, recent customers, people who have engaged with you in other ways. Positive engagement early on is the strongest signal you can create. Avoid starting with an old list that has not heard from you in a long time, because that group tends to produce bounces and complaints.
Only mail people who have given permission. Marketing consent rules vary by country and change, so check what applies to you; this is general information, not legal advice.
An illustrative ramp
The numbers below are an example only, not a recommendation for any particular service. Suppose you want to reach a list of 10,000 people.
| Stage | Emails sent | Running total |
|---|---|---|
| Day 1 | 100 | 100 |
| Day 3 | 250 | 350 |
| Day 5 | 500 | 850 |
| Day 8 | 1,000 | 1,850 |
| Day 11 | 2,000 | 3,850 |
| Day 14 | 4,000 | 7,850 |
| Day 17 | 2,150 | 10,000 |
Each step roughly doubles the previous one, and the last step simply covers the remainder: 10,000 minus 7,850 leaves 2,150. In practice you would pause or slow down whenever the numbers look worse, and a ramp for a larger or smaller list would take longer or shorter. A small business sending to a few hundred people may not need a schedule at all, just a sensible first send to the most engaged group.
What to watch while ramping up
After each step, check:
- Bounces: A rise in hard bounces suggests list quality problems. Remove those addresses before the next step.
- Complaints: Even a few complaints early on matter more than later. If they appear, pause and review who you are mailing and what you are sending.
- Engagement: Clicks are the most reliable signal. Opens can be inflated or hidden by some mail apps.
- Placement: Use seed addresses at different providers to see whether mail lands in the inbox, a promotions tab or spam. Your email metrics reports may show deferrals or blocks.
If something goes wrong, do not push through. Go back to a smaller volume and the most engaged group, fix the cause, then resume.
Keep the content steady
During warm-up, keep your messages simple and consistent. A recognisable sender name, honest subject lines and a clear unsubscribe link help. Avoid big images with little text, many links, or sudden changes in design. A welcome series is a good first thing to send, since new subscribers tend to expect it and engage with it.
Do not stop and start
Sending in bursts followed by long gaps can undo some of the benefit of warming up. After you reach full volume, aim for a fairly regular rhythm. If you know you will send much more at certain times, such as seasonal promotions, increase volume in steps beforehand where you can.
Reputation is ongoing
Warm-up is only the beginning. Over time, your sender reputation depends on how recipients react. Keep removing bounces, honour unsubscribes quickly and watch complaints. If a new domain will replace an old one, avoid moving everything at once; run both for a period and shift volume gradually.
Outcomes vary between senders and providers, and rules change, so treat any schedule as a starting point and consult the current guidance of your email service and mailbox providers.