Email Throttling & Warm-Up

How to warm your domain with Email Throttling

There are many different hurdles an email has to overcome to make it into the hands of your customers. The reputations 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. Do not increase sending volumes too quickly within a short timeframe.
  3. Keep user complaints i.e SPAM as low as possible.
  4. Reduce the number of bounced emails.

OneSignal Email

If you are using a third-party ESP to send messages, you need to manage the reputation of both your IP address and your sending domains. If you are using OneSignal's managed 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.'

Email Throttling

To warm up your IP address and domain, you'll need to throttle your email send rate and follow the schedule outlined below. Emails are throttled and released every second over that period of time.

Navigate to Settings > Messaging and enable Email Throttling. Set the limit for the total number of messages you'd like to send per day for each sent notification.


Email Throttle Setting

Analyze your recent send volume for the previous day or month, then update your throttle amount to the right threshold. If you notice a considerable number of failed emails, lower the number.

In the dashboard, you will see that messages are throttled when launching a campaign.


Notification on Message Send

Warm-Up Best Practice

When warming a domain or subdomain, you will want to keep email sending slow and steady at first, gradually increasing your sends over the first few weeks/months. The Warm-Up Schedule below shows a good conservative warm-up schedule.

Generally, the options are:

  1. Send emails every day, gradually increasing the throttle per day.
  2. Incorporate the Journeysfeature or automated messages to help increase the sends per day
  3. Create lists. This can be done with our CSV List Upload or target emails via our API directly.

Journeys are generally recommended for welcome and re-engagement campaigns and will also help send slowly as new emails get added and users become inactive.


Throttling only affects email campaigns

Time-sensitive emails scheduled through automation, journeys, or API on a one-off basis will not be throttled. When looking at a total warm-up schedule, you will need to account for the fact that transactional messaging will not be throttled in the throttling schedule and calculate your throttle schedule accordingly.

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.



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 throttling amount to align with your recent sending habits, then increasing it again by 20% a day.

1620% increase in send volume daily