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A complete email IP warm-up guide in 2023

02 August, 2022 | 26 Min Read

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Delivering email isn't as easy as you would expect, and one of the components that make things particularly tricky is IP addresses. There was a time when inboxing almost solely depended on how good the reputation of your IP addresses was. In this guide, you will learn what an IP address is, the IP warm-up process, the warm-up schedule, tips and tricks on getting it right, sender reputation, spam traps, and an additional list of methods that aid in this process. Suppose you recently purchased Spotzee Bulk Email Delivery Service. In that case, this is an excellent guide because it allows you to learn how to achieve high volume email sending while following the best practices that guide you in achieving high deliverability. This guide DOES NOT apply to low-volume senders. If you are sending below 100k emails per month, we would highly recommend you to stick with our shared IP pool.

Some advantages of sending from your IP address include protecting yourself from the reputation of other senders who might not be outputting the high-quality emails you tend to and sending large email volume by building your reputation as a sender. So you might wonder how one can tell if an IP address has been warmed up correctly or not. For that, look at the metrics like rejection or bounce rate. A high rejection rate indicates that ISPs are not comfortable receiving the volumes you are sending. It also tells you to slow down and build your reputation from the point they are rejecting your email. For example, you might see a spike in rejection or bounce rate after sending 72,288 emails daily. This tells you that you need to warm up from 50,000 emails forward and build your reputation by sending to highly engaging contacts, and this threshold slowly starts to increase.

What is an IP address?

IP is an abbreviation for Internet Protocol. Any device capable of communicating via the Internet will receive an address. This unique address allows you to communicate to that assigned device. The address is like the location of your home. If your friends want to visit your place, you will give them your address. They type it into their maps or GPS application and navigate their way to your house.

Similarly, IP addresses allow us to reach websites, chat with others, play games, and more. Our website also has a unique IP address, but it is easier to navigate to our site by typing in ‘’ than to type in its actual IP address. Both will let you end up at the same place. Without getting too much into networking, there are a few words that you need to understand before you can make sense of how IPs work. They are words like router, route, network, and bridge. A name is what we seek, address is where it is, and a route is how to get there. For example, when you send an email, you are essentially sending ‘packets’ of data across two networks - from the sending to the receiving network.

When you hit that send button on Gmail to a friend who uses, for example, Hotmail, Gmail is essentially utilising their network to send that packet of information across to Hotmail’s network. Since they are communicating over the network, what do you need? An IP address just like we talked about earlier. We use an IP address from sending network to share with another IP address on the receiving network. They exchange this data, which is how you receive or send emails. Since Hotmail knows that the IP address belongs to Gmail, it will accept that data. If some random IP tries to spam the Hotmail network, they kick them out by blocking their sending IP address. It works similarly across all the major ISPs like Hotmail, Gmail, Yahoo, and AOL.

New IP addresses trying to communicate across the network always raise suspicion. It’s like random strangers chatting with you. You always view them with caution. If they talk too often, you start to block them. Similarly, the concept applies when trying to email with a brand new IP. ISPs are cautious of the emails you are trying to send to their customers. If their customers (receiving contacts/subscribers) don’t like what they see, they avoid opening or interacting with your email. Or worse, they report you as someone who is sending spam. ISPs react to those complaints by throttling (limiting the number of emails they accept from you - the IP address) or blocking you so you can’t send to their network of IPs anymore.

Shared vs Dedicated IPs

An IP address can be shared or dedicated. You can use a single IP to send millions of emails, so most email service providers (ESPs) tend to utilise the same IP to send an email on behalf of multiple customers. This is what we refer to as a shared IP. A dedicated IP is an address allocated to a single customer. There are advantages and disadvantages to both. Let’s look at some of the benefits of sending with shared IPs. With shared, you are almost riding on the reputation of the senders using that pool of shared IP addresses. So if you have excellent senders, their reputation almost passes to the emails you send. The opposite is also true where if the group of senders are bad senders, your emails will be affected by it adversely. Your reputation starts to plummet with no fault of your own.

On the other hand, a dedicated IP gives you control over your sender’s reputation. If you send high-quality emails to subscribers who actively engage with what you send, you are likely a favourite of ISPs. It is a good idea to get your IP if you are sending at least>100,000 emails per month. It is also helpful in sending a large volume of emails since a higher reputation gives you the ability to have an excellent email acceptance rate from large ISPs. This goes back to what we said earlier, where an improperly warmed-up IP increases rejection rates. The warm-up process allows ISPs to determine your reputation, so it’s a nice little circle to keep in mind. A Higher IP reputation enables you to send a greater quantity of emails, and you will see lower rejection rates and higher acceptance rates (vice-versa).

Use cases for multiple IP addresses

There are a few use cases where one would benefit from using multiple IP s for delivering their email campaigns. Below is a list of the most common use cases that justify using different IPs. But before we go there, the number of IP addresses you need is probably one of the most asked questions concerning email deliverability. Unfortunately, there is no correct answer. We have seen senders use one single IP to send millions of emails daily and those who benefitted from spreading the load across multiple IPs and multiple virtual pools. As a general rule of thumb, if you are a high-volume sender, we highly recommend using dedicated IP as opposed to a shared one. A dedicated pool of IPs allows you to spread your email delivery over multiple IPs and helps achieve more excellent email deliverability.

To give you an example, when you are sending an email to Yahoo, occasionally, you would see a temporary deferral message where emails coming from a particular IP is ‘suspended’ for a while because of a complaint from one of the users who received their email using this IP address. If you had only a single IP, your SMTP would have to keep retrying using the same deferred IP, but if you had multiple IPs, it could make use of an IP that is not blocked by Yahoo and keep the email processing queue moving.

High volume email sending

Multiple IPs can come in handy if you send over 100,000 emails monthly. This is more true if your email campaigns are time-sensitive (Eg. deadline sales and time-based offers). If you need the email arriving in your recipient’s inbox on time, we highly recommend using more than one dedicated IP. However, as per the Yahoo example above, if you send 300,000 emails that you need to deliver within a 6-hour time frame, then doing so with a single IP address is almost impossible. Furthermore, sometimes receiving email exchange servers restricts how many concurrent emails they receive from your IP, which would further limit your throughput in addition to temporary deferrals due to complaints. In the end, it ultimately comes down to the nature of your business and your requirements.

Transactional and marketing streams

The best practice is to use different IP addresses to send your transactional and marketing emails. A transactional email is an email sent to a single individual recipient based on actions possibly taken by that recipient, such as purchasing an item from your online store or requesting a password reset email. Because the user’s actions initiate them, they are also the kind of emails that receive a small number of bounces and complaints. As a result, the engagement rate for transactional emails is generally relatively high. They are also non-promotional, which also helps. For this reason, it is best to seperate these two streams of emails to ensure the reputation of your transactional IP pool is spotless to ensure high deliverability. You don’t want to lose a customer because they can’t use your product as the requested password reset email never comes through.

You can further seperate out IPs by domains used for sending as it tends to lock in the domain reputation to that assigned pool. Separation by domain benefits larger companies with several brands they use to deliver goods and services. For example, ISPs like Google Mail (Gmail) focus more on domain reputation than IP reputation. Most ISPs now follow this route as multiple companies with varying reputations can use a shared pool of IPs. For example, suppose an email service provider like Spotzee allows their customers to use their shared pool. In that case, any new senders could potentially cause issues in deliverability for the rest of the customers on that same pool. For this reason, most ESPs are cautious not to put high-volume senders on these shared pools.

When not to use dedicated IPs?

As we discussed above, if you send less than 100k a month, you are probably okay with using a shared IP pool. However, we do not recommend getting more IPs to help your sender’s reputation. Many marketers believe that having more IPs will help them with deliverability. It doesn’t. It is not a good reason to have a dedicated pool. We often see the opposite happening where the ISPs are unhappy seeing you send from another IP because your IPs are throttling. The reason it’s not a good idea to add more IPs to spread your email volume is because many ISPs look at the email content and the domain it is coming from rather than the IP it uses to send that email. If your sender’s reputation declines, you are better off looking at ways to improve it. We have a guide on how to do that. Alternatively, you can get in touch with our Spotzee Marketing team, and we will point you in the right direction.

Why and when do we warm up a new IP address?

Let’s think about this from an ISP’s point of view. An IP address can deliver large volumes of emails - enormous network packets requiring a response. So ISPs are cautious and suspicious when they do not know who it is. They have no idea who the sender is and if they are good or bad. It’s like talking to a stranger in real life. Another issue relating to this unexpected IP email volume is the typical behaviour of spammers who hop from IP to IP (domain to domain). They are relentless in their sending and do not adhere to the best practices. They get straight to mailing, sometimes without giving subscribers a choice to unsubscribe.

ISPs need a sending history to base their decision on; for a new IP, that’s a blank slate. For this reason, ISPs protect themselves by deferring or blocking messages from an unknown or new IP. That’s one of the reasons we invest so much time in building this sending history with each ISP (Yahoo, Gmail, AOL etc.). By doing that, we gain a sender’s reputation to prove to them that you are an excellent sender following the best industry practices. You do this by increasing the emails you send daily to your most active subscribers. Think of them as trust levels. For example, if Gmail has accepted 500 of your emails on the first day and they see that your contacts are engaging with the email you sent them, they would be happy to receive a little more the next day. However, if you decide to bombard them with 5000 emails the next day, that will make them defer and block your emails.

You slowly work your way up to prove you are a good sender. We have various strategies listed below that show you a rough schedule you can follow. The plan showcases how many emails you should send on day X and build the sender’s reputation with your dedicated IP pool. By following the guide, you are proving to the ISPs that you are a genuine sender and that your emails are okay to receive. Slowly working your way up is time-consuming, but it is worth it if you want to send millions of emails eventually. A good example is Amazon, which sends around 33,000 emails per second on Amazon Prime day to their customers worldwide with their pool of IPs. The ISPs accept those millions of emails without issues because they would have built their reputation over time rather than sending that quantity from day 1.

Warming up new IPs is recommended when moving to a new SMTP relay provider or when using a new IP by adding it to your existing pool. However, it would be best to remember that warming up affects your domain’s reputation. The more warm your IPs are, the more you gain the trust of ISPs. The domain reputation works the other way around too. If your domain name has a fantastic reputation with ISPs, your warm-up period would be much shorter and sharper than the traditional schedule listed further down this article. Do note that you do not need to warm up your IPs if you are on a shared pool. Like we said earlier, this guide only applies to senders considering having their own dedicated IP or IP pool.

What is the process for warming your IPs?

We covered everything from what an IP address is when you need one, the difference between shared and dedicated, and when you need to warm up. Now it’s time to get into the actual process of warming up your IP addresses. But, before we start, you need a few things to ensure you get this right.

Domain authentication

Email technology has been around for a very long time, and while there are positives, there are some negatives too. One is that anyone with an Internet and IP address can send emails to anyone else. They don’t need any authorisation. So, for example, you can send an email from ‘’, which would go through just fine. So anyone on the Internet can email anyone just by knowing their email address. But unfortunately, the capability of anyone sending email gave rise to enormous amounts of spammy emails from marketers without consent or permission. Domain authentication implements a process to tackle that by allowing companies to authenticate who they are and sign off their emails to show that they were sending them and not anyone random on the Internet.

These authentication protocols tell ISPs who the sender is because the email could have arrived from any third party without them. No reputable ISPs would allow unauthenticated emails to their users’ inboxes. So as a sender, you must ensure you have set up proper email authentication as it shows you are a reputable sender with honest intentions. Furthermore, it instantly improves the trust the ISPs place in your sending domain and your company. There is no use in warming up your IPs without these. There are two protocols to consider - SPF (Sender Policy Framework) and DKIM (Domain Keys Identified Mail). An SPF check will allow ISPs to validate who you say you are without going into too much detail about how it works. DKIM stops your emails from being tampered with by signing the messages through encoding in the email header.

Even with the SPF and DKIM working well, there were still a few loopholes in the authentication process. To address those loopholes, there was the introduction of a newer protocol known as DMARC that helps improve deliverability. It stands for Domain Message Reporting and Conformance. Setting up a DMARC record allows ISPs to send feedback when DMARC fails. For example, as a sender, you can request ISPs to reject, quarantine, or do nothing with the incoming email when it fails the DMARC. While it is ultimately the decision of ISPs, it gives marketers transparency and conformance to best industry practices. It is also a tremendous investigative tool to look into anyone spoofing your domain and using your company domains. Having DMARC in place and processing the feedback allows you to understand better the rise in rejections or failure in sending emails to various providers.

Highly engaging emails and subscribers

Engagement is key to the success of your warm-up. If you are sending to a bunch of contacts who are likely to avoid seeing your email or click on the ‘report spam’ button, you failed before you even started. Warm-up only works when you have a decent number of engaging subscribers who enjoy receiving your content and show their enjoyment via opening and clicking the links on your email. These are trackable by your marketing software and ISPs keeping watch over these outgoing traffic. One of the easiest ways to send to this engaging list of subscribers is by using a feature often offered with nearly every email marketing software and referred to as ‘segmentation’.

Segmentation is the process of dividing up your subscribers based on specific criteria. For example, let’s say you are a pet food supplier, and you might have a link in your campaign that says, ‘Click here if you like dogs’. A subscriber takes action by clicking here, and it goes to a page on your website that gives more details on dogs. Most software allows you to put contacts who clicked on the dog link into a specific group, segment, or mailing list. Now you can use that group, segment, or mailing list, to send our highly targeted email campaigns relating to dogs rather than all pets. You might ask why this is important in the warm-up. Sending highly personalised campaigns based on subscribers’ preferences makes an email campaign successful. It’s what your contacts would most likely engage with (opens and clicks), and that’s what you are after when trying to warm up your IP addresses.

You can go through your historical data of opens and clicks and segment them into various lists or groups. You can then create these highly personalised campaigns that target those groups. It is considered one of the best ways to increase your open and click-through rates. Most software also offers automation where you might send a campaign when a contact clicks on a particular link or opens an email. Some companies call this a playbook of how you will play it out for a potential lead, from expressing their interest to getting them as your customer. This process of sending engaging automated emails is excellent for using new IPs since you know your contacts are highly likely to engage with them.

It’s also a good idea to weed out subscribers who haven’t engaged with your content. So, for example, most companies use the last login date and time of a customer to decide whether to continue engaging or stop. It’s also a great way to find your most likely to engage subscribers. The use of email marketing automation can help you greatly in emailing your most engaged audience by sending to people with historically high open and click rates. You can use these audiences to send more than one email with a gap of a day in between, for example. The other most important thing to note is spacing these campaigns out. You don’t want to lose your good subscribers by emailing them too often. So to avoid losing good subscribers, large corporates often ask their customers how often they’d like to hear from them.

A typical warm-up schedule with email volumes

Warm-up methods

There are two main proven methods of warming up your IP addresses:

  1. A warm-up period where you only send once to each engaging contact on your mailing list
  2. A warm-up period where you send a different email message every day to all your contacts but add a few extra you haven’t messaged previously

The number of emails you send depends on your chosen schedule, but it is usually double what you sent the previous day. Then, you continue adding a few new contacts daily until you reach your entire mailing list. Both these methods ultimately help you reach your warm-up goals, but the way you get there is a little different. The way to pick one of these methods is to look at the way your company currently engages. For example, your company might send daily news updates. In this case, the second method might work best for you.

Here are a few schedules that ESPs suggest:

An few warm-up schedules

The most important thing to understand here is that ISPs work differently. For example, you might find that Yahoo warmed up far more quickly than Gmail, which is normal. If you are serious about getting this right, we suggest you segment your list based on ISPs. For example, you might have all Yahoo-related emails in one segment. By doing this, you can individually target each ISP and warm up based on responses you are seeing from them. If you see that they are throttling you after a certain quantity, like mentioned above, it is best to repeat the volume of emails until they accept them without issues. After that, you can move to the next day’s quantity.

Bulk emailing your contacts at Yahoo, AOL, and Gmail clears up after a few sends with positive engagement metrics, but the actual inbox delivery might delay. The key is to continue sending to your most engaged subscribers. The delays (421 bounces) at AOL, Microsoft, and Comcast will retry after 72 hours, and if not delivered within that timeframe, they will bounce as a 5XX code. The message is to expect delays that lessen as your reputation develops over time. See our comprehensive guide to email metrics.

Here’s an example IP warming plan based on ISP

An example warm-up schedule based on ISPs
DayMicrosoftGoogle MailVerizon (Hotmail & AOL)Others
↑ Increase by 5%↑ Increase by 5%↑ Increase by 10%↑ Increase by 20%
↑ Increase by 10%↑ Increase by 10%↑ Increase by 20%- Stay at 20%
↑ Increase by 20%↑ Increase by 20%↑ Increase by 40%↑ Increase by 40%
↑ Increase by 40%↑ Increase by 40%- Stay at 40%- Stay at 40%

Setup your strategy

Spotzee supports customisable warm-up plans that work for your business: You can create segments using an advanced filter accessed by going into the lists page and then choosing “All contacts”. You can click on the “Filter” button to bring up advanced filtration options. You can segment based on various attributes, including custom field data. After this, you can create a warm-up plan by going to Warm-up plans -> Create new.

From there, choose your strategy, and you can attach your delivery server to this plan you’ve just created. Now, set up your email campaigns to be sent through that delivery server. Voilá. You are good to go. This automatic IP warm-up process ensures you never send more than your schedule allows making it perfect to set and forget. ‘Set and forget’ does not mean you don’t have control over it. You are free to make changes to suit your needs and go back to that page to see how the warm-up process is going.

Track your performance

You are almost there now that you have configured your campaigns and the warm-up plan. Well done! Now it’s time to monitor. IP feedback monitoring is a crucial step in the success of your IP warm-up process. It’s like setting up this fantastic start-up web app, but if your customers aren’t able to sign up and you are not monitoring your error logs, your start-up is heading towards failure. It is essential to keep watch during this phase since it is better to be proactive than reactive. A few indications will give you an idea of whether the process is smooth sailing.

One of the first things to monitor is engagement. Are the subscribers you have segmented and engaged with responding well to your campaigns? If they aren’t, it’s probably time to do some A/B testing and just your campaign content, subject line, and other elements to ensure it performs well. Another aspect to look out for is how each ISP is doing in line with the quantities you sent. Remember, the email is a global network, and ISPs do rely on data provided by third-party to make decisions on your email. If you are on the blacklist, we suggest you do not send from those IPs and work towards getting your IPs removed from those before putting them back on the warm-up.

Some other metrics to keep watch on include your bounce rate, complaint rate, unsubscribes, open rate, and click-throughs. For example, if your bounce rate has increased, look through your bounce report that Spotzee generates and see the reasons. Likewise, if your unsubscribes are on an incline, some likely causes could include subscribers not enjoying the content or the frequency of your emails. Finally, a drop in click-through rate could suggest that your audience is not enjoying the content and could signal a decline in the sender’s reputation.

We provide several tools to check for the validity of the HTML email code, spam assassin score, and wording. In addition, most large ISPs offer free tools to help you review your sender’s reputation and deliverability rates. For example, Google Postmaster is a handy tool that shows the reasons behind your sender’s reputation scores. Most provide data on authentication failures, user complaints, and ways to improve via helpful articles. They also list the error codes they respond with and what each means — most ISPs’ portals gauge how they see you as a good, medium, or bad sender. If your metrics look good, you can slowly start adding your less-engaged subscribers to the mix but make sure you DO NOT add your non-engaged users. Doing so will ruin your efforts.

If you keep tracking your metrics, scaling the email volume and repeating, you will have a stellar IP reputation in no time with all major ISPs. You might often repeat the same volume a few times before going to the next day’s volume. Don’t worry, that’s quite normal. Following the process highlighted here will ensure you land in the inbox, and the ISPs will be happy to receive your email.

Quick pointers

  • Scrub your lists - Remove all users who have complained, unsubscribed, hard-bounced or are inactive. If you haven’t emailed subscribers in a while, run them through email validation services that Spotzee provides or our in-house email validation solution. Running them through such services will help you eliminate spam traps that can damage your reputation as a sender.
  • Be patient - Warming your IP addresses is a slow process. As they say, all good things take time. Make sure you stick to your warm-up schedule. Changing your schedule halfway through the warm-up operation is a bad idea.
  • Email volume - Don’t increase your volume based on your IP number. If you have 4 IP addresses, it does not mean you do four times the warm-up schedule unless you use four different domain names. You are warming up your domains alongside your IPs.
  • Send consistently - Send regular emails to your subscribers. If you miss a day, start from where you left off. Don’t push your luck by sending the volume you didn’t send the day before. ISPs will notice this spike and start to throttle you. Consistency is the key.
  • Personalise everything - Highly engaging campaigns have highly personalised content valuable to your contacts. Higher personalisation often drives higher open and click-through rates. Higher engagement rates thereby determine your sender’s reputation.
  • Delivery server balancing - Split your campaigns to be handled by your new IPs server and your warmed-up delivery server. By splitting your volume to go to both, you are ensuring the least disruption to your outgoing email campaigns and a seamless transition from older IPs to newer IPs.
  • A large IP pool is bad for business - Many senders think rotating their large pool of IP addresses will let them send the volume they desire, but it is something ISPs keep watch on (known as snowshoeing). If you warm up your IP well, you can send millions of emails without issues.
  • Avoid sending to spam traps - The easiest way to avoid them is by not purchasing or renting lists, removing hard bounces, continuously re-engaging with inactive subscribers, and getting rid of unengaged subscribers regularly.

We hope this guide has provided you with helpful information on IP warm-up process, and we hope you’ve learned ways to warm up correctly and get a great start on email marketing. At Spotzee, we aim to provide a vendor-agnostic email marketing automation tool. We aim to introduce every form of marketing into our platform so you can get a whole omnichannel marketing experience. If there is something you believe we have not covered in detail, let us know, and we will update the guide to include those topics.

Spotzee Marketing platform lets you focus on your business than owning and maintaining an expensive email infrastructure. We help companies of all sizes with technical details (Eg. Setting up SPF and DKIM). We also offer world-class deliverability expertise to help your emails reach the inbox. With a fully-featured email marketing platform, you can choose to connect the email providers you like and also add our bulk SMTP service. In addition, our expert consulting team provides ongoing help for all your email needs and helps you 24/7. Talk to us today about your email needs.

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