What is IP warming?

IP Warming is designed to help you establish a positive reputation with ISPs (Internet Service Providers). Every time a new IP address is used to send an email, ISPs programmatically monitor those emails to verify that it isn’t being used to send spam to users.

What if I don’t have time to warm IPs?

IP Warming is required. If you fail to warm IPs appropriately, and the pattern of your email causes any suspicion, any or all of the following may happen:

  1. Your email delivery speed could be significantly throttled or slowed.
    • ISPs throttle email delivery when suspicion of spam arises so that they can protect their users. For example, if you send to 100000 users, the ISP might deliver the email only to 5000 of those users over the first hour. The ISP then monitors measures of engagement such as open rates, click rates, unsubscribes, and spam reports.
    • If a significant number of spam reports occur, they might choose to relegate the remainder of that send to the spam folder rather than delivering it to the user’s inbox.
    • If engagement is moderate, they may continue to throttle your email to collect more engagement data to determine whether or not the mail is spam with more certainty.
    • If the email has very high engagement metrics, they may cease to throttle this email entirely. They use that data to create an email reputation that will eventually determine whether or not your emails are filtered to spam automatically.
  2. Your domain and or IP could be blacklisted by the ISPs, at which point all of your emails will begin going directly to the spam folder of your user’s inbox.
  • If this occurs, then you can scan your host IP to any DBLS ISPs to get off those lists according to their policy.

IP warming best practices

All of these consequences are entirely avoidable if you follow the following guidelines:

  1. Start by sending small volumes of email, and increase the amount you send each day as gradually as possible.
    Abrupt, high-volume email campaigns are regarded with the most skepticism by ISPs. Therefore, you should begin by sending small amounts of email and scale gradually towards the volume of email you ultimately intend to send. Regardless of volume, we suggest warming up your IP to be safe. See the following schedule for details.
  2. Ensure that your first content is highly engaging and maximizes the likelihood that users click, open, and engage with your email.
    Always prefer well-targeted emails to indiscriminate blasts when warming IPs.
  3. When IP warming is complete, continue sending as consistent a cadence as possible.
    IPs can cool down if volume stops or significantly decreases for more than a few days.
  4. Spread your email sends across a day or several days.
    Spread your send across a longer timeframe, rather than sending a mass blast at a single specific time.
  5. Ensure that your email list is clean and doesn’t have old or un-verified emails.
  6. Carefully monitor your Sender Reputation while you conduct the IP warming process. You can try these tools for sender score reputation check.

IP warming schedules

This schedule is based on an example idea. If your system is just got ready and a few days old then you can reduce the value as you want. But don’t go above this. It’s also important that you don’t skip days as consistent scaling improves deliverability.

Day# of Emails to be Sent
150
2100
3500
41,000
55,000
610,000
720,000
840,000
970,000
10100,000
11150,000
12250,000
13400,000
14600,000
151,000,000
162,000,000
174,000,000
18+Double Daily Until Desired Volume

Once warming is complete and you’ve reached your desired daily volume, you should aim to maintain that volume daily. Some fluctuation is alright, but reaching the desired volume, then only doing a mass blast once a week may negatively affect your deliverability and sender reputation. Lastly, most ISPs only store reputation data for 30 days. If you go a month without sending, you will have to repeat the IP warming process.

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