IP Warming- Do It Right Or Do It Twice


For 2022, Webbula is launching a series of blog posts about email deliverability topics. We have a variety of esteemed authors from the email industry lined up to participate. 

  • Subscriber Management: How to Start, Maintain, and Break Up by Elizabeth Jacobi. Read it. 
  • Email Opt-Ins: It's All About Consent In the End by Matthew Vernhout. Read it here. 
  • Email Authentication 101: What It Is And Why It Is Important For Brand Reputation by Yanna-Torry Aspraki. Read it here. 
  • Why Blocklists Make Us Better Email Marketers by Andrew Kordek. Read it

Watch the discussion


By far, IP warming is the topic I am asked about the most at work. For something that is so fundamental to a healthy email program, I’ve noticed a distinct lack of knowledge (and a little hubris) surrounding the subject. Though it can be daunting and time-consuming, understanding why IP warming is so important helps temper some of the frustration at having to do it. 

At its core, it's fairly simple: sending on a new IP (or a new domain, but that’s a different article) should be done methodically, beginning with a low volume of your most engaged subscribers. Over time, that volume should slowly be increased in order to build your sending reputation, allowing mailbox providers the opportunity to monitor your behavior and determine whether you are a trustworthy sender.

Think about it like this- you want to throw a party and invite your friends, but your friends want to invite some of their friends that you don’t know. You’d want some assurance that they won’t trash your house, right? An oversimplification for sure, but it’s one I hope most people can relate to.

I used to try and come up with analogies like this to help people understand just how important IP warming is and why it should not be skipped or rushed; it’s only human to think you may be an exception. These days I just respond with background and facts - Do you know who sends out large amounts of mail on new sending infrastructures without warming or taking into consideration their audience? Spammers do

The truth is that there are no shortcuts when it comes to building a good sending reputation. IP warming is non-negotiable if you don’t want to be labeled a spammer, have your mail blocked, and your reputation trashed.

Mailbox providers want to protect their ecosystems and users from this type of behavior and mail, so they keep a close watch on new IPs' sending practices. By warming that new IP, you're taking the first steps towards building that all-important trust. While “low and slow” sounds simple (there’s quite a bit of nuance involved), it’s basically the driving principle of IP warming. 

So, what are some of those nuances? While the following points aren’t exhaustive, they do cover the fundamental components of IP warming.

6 Fundamental Components of IP Warming


1. Reputation


First, it’s important to establish just how reputation is determined and influenced. While we don’t know everything about how mailbox providers attribute reputation to a sender, we do know that both positive and negative signals contribute to their decisions and that these signals should be taken into consideration. 

Positive signals lead to a strong reputation, resulting in a high percentage of email being delivered to the inbox. These signals include:

  • Sending to recipients that have directly opted-in with your brand. 
  • Positive recipient interaction (clicks, adding your address to their safe sender list, starring the message, saving it to a folder, etc.)
  • Low number of invalid and inactive email addresses
  • Low complaint and bounce rates
  • Engagement parameters to make the mail most relevant to users
  • Though it does not guarantee inbox placement, authentication standards should be fully configured

Negative signals result in a poor reputation, meaning a high percentage of email is being  filtered to the spam or blocked outright. These signals include:

  • Lack of permission or lack of direct opt-in.  If recipients do not want your mail, your reputation will suffer
  • Negative recipient interaction (submitting spam complaints, ignoring the mail, deleting without reading, reporting as phishing, etc.)
  • High number of invalid and inactive email addresses indicating poor list quality and hygiene
  • Large amounts of spam complaints, bounces, and unsubscribes
  • Large spikes in volume
  • Spam trap hits
  • IP and domain blocklistings

2. Planning


Planning ahead is crucial. Attempting to cram six weeks of IP warming into two is a recipe for disaster, so make sure you give yourself plenty of time to not only craft and execute the plan, but also to course correct if necessary. 

The amount of time needed to warm will depend greatly on volume and data quality (among other factors), though it’s fair to say that the more complex the plan, the more time you will need. The levels of difficulty can range from straightforward (adding a new IP to your pool and slowly moving volume over to it) to the more complicated (an ESP migration or a multi-stage, multi-IP plan tailored to each of the different mailbox providers contained within your intended audience). 

While I would hesitate to leave less than 1 month to plan and execute a more straightforward, lower volume plan, a more complicated plan might require double or triple that time. It all comes down to the details.


3. Audience


It’s recommended to clean your list before warming to weed out any invalid or bad addresses. Also, it’s important to be honest when identifying your engaged audience. You can always go back and fold in less engaged contacts once you’ve finished warming when the stakes are lower, but it’s best during IP warming to stick to those users who have not only shown unmistakable signs of interest in your content, but who have also opted-in directly. Additionally, while past engagement is important, you want to make sure the audience you are selecting will ensure that engagement will remain strong throughout the IP warming process.

The average volume from the past 6 months of sending can be used as a rough guide for your warming volume, though if you have a particular audience in mind to target (as long as there is a high chance they will engage), that can also be used as your target volume. 

When you’re building your daily segments, begin with your most engaged subscribers, gradually introducing those that are less engaged, starting low, around 7-14 days last engaged, and increase in increments of 15 days or so (30 days, 45 days, 60 days, etc.) If volume allows, I like to recommend sticking to users that have engaged in only the last 90 days. At most, I would not go beyond 180 days engaged during warming since there are some mailbox providers that consider people that haven’t engaged in more than 6 months to be inactive. 


4. Content


When choosing content to send during warming, review past campaigns for evergreen content with high rates of engagement. This content can be used as a model for what you will be sending during warming. While this can help boost engagement, it isn’t foolproof. Sometimes it’s necessary to make adjustments to content during warming if it isn’t generating the level of engagement you were hoping for.


5. Low and Slow


Though you can probably safely start at a higher Day 1 if you’re working with users with really strong engagement, I tend to err on the side of caution and recommend a Day 1 volume around 250, especially when working with senders who do not have much experience warming (and are therefore probably creating a less complex plan).

From there, slowly increase the send volume day over day, no more than doubling the previous day’s volume. As you start to reach segments of your list with lower, less frequent engagement, I recommend to slow the rate of increase to 1.5 times the previous day, though if you are not seeing declining performance, you can continue to double.

You can choose to send every day during your IP warming process, 5 days a week, or according to the sending schedule you normally keep (ex. Monday, Wednesday, Friday), but it’s recommended to not skip more than 4 days in between sends during warming.Whatever you choose, it’s important to be consistent.


6. Monitor (And Be Prepared To Pivot)


Review the campaign results at the mailbox provider level daily for engagement, complaints, delays, bounces, and unsubscribes, keeping in mind that having some deliverability issues at the start of warming is not unusual since there is no sending reputation yet on which providers can base their judgments.

Also, be prepared to see inbox placement that is lower than you are used to. Again, this is due to the new IP’s lack of sending history. Mailbox providers are likely to filter some email to spam in order to observe how their users react. This is all part of the normal process of establishing reputation. Inbox placement will increase over time provided recipients are responding using positive signals.

In addition to those positive signals, the quality of your audience, the speed of your sending, and your adherence to deliverability best practices are also determining factors. If you are not following best practices, the deliverability issues will likely continue throughout the warming process, taking even longer to warm.

Delays during the first days of warming are also normal and will decrease each day as a good reputation develops. If the mail is ultimately being delivered, there isn’t too much cause for concern. However, if the sends are timing out in large quantities, decrease your volume to that mailbox provider and throttle that volume by spreading out the sending over a few hours. 

Blocking may occur if your subscribers are not engaging with your emails (or are engaging negatively) or if you are going over the daily volume caps recommended in the warming plan. If this happens, scale back on volume to that provider and focus on the most engaged users, slowly ramping that volume back up. 

One final thing to keep in mind- just because you are finished warming up to your high volume, doesn’t mean mailbox providers aren’t still holding you to a higher level of scrutiny. It’s necessary to not only continue following best practices but also to continue sending. You should have a long term plan in place to maintain a certain level of volume, otherwise your IP will cool and you will need to warm all over again.

As I said earlier, while this is an oversimplification, having an understanding of the reasons warming a new IP is necessary will help guide the creation and execution of a warming plan. Building a strong reputation and reaching the inbox is all about following those deliverability best practices.


About the Author


Amanda Jackson

Amanda Jackson has worked in the deliverability and compliance world for 10 years and is currently an Email Deliverability Consultant at Iterable.




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