Email Warm Up

How to warm your domain for best email deliverability.

There are many different hurdles an email has to overcome to make it into the hands of your customers. The reputation of your domain and sending IP address are crucial for email clients (i.e., inboxes) for determining if they should deliver the email or flag it as spam.

To prove that you are not a malicious sender, you must demonstrate consistency in your email-sending habits. OneSignal helps increase your domain reputation through a process called email warm-up.

Domain & IP Reputation

In an effort to reduce spam messages, email clients will rate-limit emails by bouncing or dropping them before delivering them to your recipient's inbox or placing the email in their spam folder.

To increase your sending reputation, you should:

  1. Have consistent sending volumes. Email clients typically look at the last 3 - 4 weeks to determine what your maximum send volume was.
  2. Focus email sending on recipients that have high levels of engagement from opening and clicking emails. See Email Retargeting options.
  3. Do not increase sending volumes too quickly within a short timeframe.
  4. Keep user complaints i.e SPAM as low as possible.
  5. Reduce the number of bounced emails.


OneSignal vs 3rd Party Reputation Management

If you are using a third-party ESP to send messages (like SendGrid, Mailchimp, or Mailgun), then you need to manage the reputation of both your IP address and your sending domain(s).

If you are using OneSignal's email delivery, we manage the reputation of your IP address but you will still need to make sure your domain has a good reputation and is considered β€˜warm.'

Recommended Warm-Up Schedule

This is the schedule to follow for sending emails that will increase the likelihood of deliverability and reduce ISPs greylisting, rate-limiting, or blocking your domain or IP address.

1620% increase in send volume daily



Follow a 20% daily increase for your send volume from day one. If you have a period of significantly lower sending, and you want to send a message to a larger segment, we recommend lowering your sending amount to align with your recent sending habits, then increasing it again by 20% a day.

Warm-Up Best Practice

When warming a domain, you will want to keep email sending slow and steady at first, gradually increasing your sends over the first few weeks/months as outlined in the provided Warm-Up Schedule.

Generally, the best sending options are:

  1. Target email addresses directly with our Create notification API and include_email_tokens property.
  2. Create lists. If you have a CSV list of emails already, you can group that into several different segments by uploading and tagging the emails. This can be done with our CSV List Upload or Create user API.
  3. In addition, using a mixture of wait nodes and split branches in the Journey Builder can help spread your email volume.
  4. Prioritize Recipient Engagement

In the email warm-up process, it's vital to engage recipients effectively. Focus on those who recently opted in or engaged with your emails, as they are more likely to interact with your messages, this will help with boosting deliverability and sender reputation.

Monitor and Adjust Email Volume

During the warm-up, closely watch recipient engagement metrics like open rates, clicks, and unsubscribes. If engagement drops or unsubscribes spike, reduce email volume temporarily. Concentrate on improving engagement through better content, segmentation, A/B testing, and personalization.

As engagement stabilizes, gradually increase email volume based on where you are in the warmup schedule to maintain a strong sender reputation and effective campaigns.