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What is an IP warm up & Why do you need it?

Updated: Mar 29

Email deliverability can be influenced by many factors - domain reputation, email content, or even by the type of your email.

An IP address is one of those factors and if you have a new one, it can negatively influence the success of your email campaigns.

The Solution? A process called IP warmup.

This article will help you better understand what an IP warmup is and why you need it as well as show you the best IP warmup practices that you should keep in mind when warming up your IPs.

IP Warm up process

What is IP warm up?

IP warmup (or IP warming) is a process of sending emails from a new (or cold) IP address and gradually increasing send volumes according to a predetermined schedule in order to establish a positive reputation for the given IP address.

An IP address is a unique set of numbers that identifies your email domain. ISPs (Internet Service Providers) use your IP address to track and evaluate your email activity and, in the end, to determine your IP reputation.

If an IP address is entirely new, you need to warm it up first in order to achieve high email deliverability of your email campaigns.

Why is IP warm up important?

The purpose of IP warmup is to improve your IP reputation and gain ISPs' trust so all your emails can be delivered right into recipients' inboxes (and not be blocked by spam filters).

Whenever you start sending emails from a completely new IP address with zero reputation, ISPs and ESPs (Email Service Providers) can get suspicious about it and prevent your IP from delivering a larger number of emails at once until you “prove” that you are a reliable sender.

Once ISPs have some historical data about your IP address and your email activity, they will allow you to send more emails to a larger number of people - or vice versa, throttle your email volumes if you start to have a bad IP reputation.

IP warmup helps to create a positive reputation for your new IP by gradually sending a larger and larger number of emails over a period of several weeks until it's ready and properly “warmed up” for real email campaigns.

Note: It is important to understand that the IP reputation is not the only factor that can impact your email deliverability. ISPs also take into account the reputation of your email domain, subdomains, or even a specific email address when determining if or how many messages should be delivered to your recipients.

What impacts IP reputation?

An IP's reputation can be influenced by many factors such as:

  • Spam reports - the number of spam complaints that your IP receives.

  • Delete rate - the number of recipients that moved your emails into their trash folder.

  • Bounce rate - the number of emails that were not delivered to recipients' inboxes.

  • Engagement rate - the number of people who opened, replied to, or forwarded your emails.

  • Unsubscribe requests - people who unsubscribed from your email list.

  • Email content - the quality of your messages, grammar mistakes, usage of spam words, the trustworthiness of included links, etc.

  • Blacklists - The reputation of an IP address can suffer if it is put on one of the popular email blacklists.

And many other factors…

It’s important, though, to understand that not all of these components carry the same weight.

For example, the IP reputation won't be dramatically influenced if some people unsubscribe from your email list - on the other hand, having many spam reports can severely damage the reputation of your IP.

List of factors that influence sender reputation

IP warm up schedule

Warming up the IP address is an ongoing process that should have a predetermined schedule - starting with a few emails sent per day and gradually increasing the amount over the period of 30 (or more) days.

For example, if you are planning to send 1,000,000 emails per month as a part of your email campaigns, you should start with only a few dozen of warm up emails per day and gradually increase the number of emails sent until you reach your desired email volume:

In addition to the initial IP warmup process, you also need to keep sending this large number of emails on a monthly basis otherwise your reputation might fluctuate periodically.

IP warming best practices

IP warmup involves a lot of activities that can slowly (but surely) improve your IP reputation over time. Here are a few practices that you should keep in mind when warming up your IP addresses:

1. Implement email authentication

Email authentication can indicate to ISPs that your IP address is reliable and can be trusted.

Authentication allows receiving servers to quickly verify your emails and prevent hackers from spoofing your account. It also shows that you prioritize your customers’ well-being and don’t want them to be flooded with spammy messages.

The email authentication consists of 3 parts (and it’s best to take the time to complete all of them):

  • Sender Policy Framework (SPF) – A DNS record that allows you to specify authorized domains that can send messages on your behalf.

  • Domain Keys Identified Mail (DKIM) – A DNS record that adds encryption to all of your outgoing emails so the servers can see that your email content hasn’t been tampered with.

  • Domain-based Message Authentication, Reporting, and Conformance (DMARC) – A DNS protocol that uses both SPF and DKIM to assist ISPs when validating the authenticity of your emails.

2. Switch to a dedicated IP

If you’re operating on a shared IP, you may want to consider transferring your information to a dedicated IP to have more control over your reputation.

Shared IP and its reputation can be negatively impacted by other people who are using it as well - even if you would try your best to properly warm up the IP address, the IP reputation could be easily damaged by spammers or scammers who would use the given IP for their malicious email activities.

Switching to a dedicated IP address will help you to solve this issue and give you full control over its reputation.

3. Improve domain reputation

Having a positive domain reputation is as equally important as having a good IP one.

If your email domain gets a bad rep, all of your emails will be either blocked or simply end up in the spam folder - and your IP reputation will suffer along the way too.

ISPs are doing everything they can to protect their users from spam and malicious content, so if you have a less-than-stellar domain reputation, it won't matter from which IP you will be sending your emails, even if you warmed it up.

Note: If you would like to know what can impact your domain, you can read our post about email reputation with tips and tricks on how to gradually improve it.

4. Know your sending limits

Depending on the number of emails you want to send per day, you may want to look into upgrading your ESP.

We do not recommend sending email blasts from a free Gmail or Outlook account because scammers tend to use these and you will be flagged.

It’s also important to understand that many ESPs equate the “number of emails sent” with the “number of recipients.” In short, trying to circumvent the limits by BCC-ing all of your recipients on a single message won’t work.

Here’s a quick list of some of the most popular ESPs and their sending limits.

​Email Service Provider

Sending Limit (Per Day)

Gmail (Free)


Gmail (Google Workspace)


Outlook (Free)


Microsoft 365/Office 365


Zoho (Free)


Zoho (Paid)


Zoho (Custom)









150 (per hour)


100 (per hour)





Amazon SES


Proton Mail (Free)


Proton Mail (Plus)


Proton Mail (Professional/Visionary)






SendGrid (Free)


SendGrid (Essentials)

Up to 100,000 per month

SendGrid (Pro)

Up to 1.5 million per month

Sendpost (Starter)

10,000 per month

Sendpost (Growth)

600,000 per month

Sendpost (Scale)

3 million per month

5. Provide high-quality content

Writing a good and relevant email copy does not probably need an explanation - if your email content is scammy or irrelevant, readers won't click on any of your promotion links (and probably won't open your emails in the future ever again).

At the end of the day, with scammy content, you will probably get a lot of spam reports - which will hurt your IP warmup process as well as your IP reputation overall.

Although creating a good email copy is a little bit of an art and requires some marketing skills, there are a few ways how you can improve your content immediately:

  • Keep the optimal length - depending on the type of your email, you might consider creating a shorter (or longer) version of your content. In cases like sales emails or lead generation, nobody likes to read tons of text (especially if it is just a reminder of some product promotion or discount). On the other hand, newsletters or marketing emails tend to have slightly longer content.

  • Personalize the message - whether it is the name or the location of the recipient, writing a personalized email will keep the reader engaged and more willing to read your full message.

  • Make it readable - try to keep sentences short and concise, divided into small paragraphs, and with an easy-to-read font that users can quickly scan.

6. Avoid spammy words

Spam filters are sensitive to the content that your emails contain, especially for risky words that just attract attention and mislead the readers.

Due to this fact, try to avoid words like “FREE”, 75% OFF, BUY RIGHT NOW, etc., since it will just increase the chance that your emails will end up in spam folders.

The same can be applied to click-bait titles or claims in your emails that are promising some prize but in reality leading to something completely different.

Here is a list of spammy words that you should not include in your emails if you want to have a positive IP reputation (collected by Mailjet):

List of spammy words that impact IP reputation

7. Maintain regular conversations

Creating positive engagement and getting responses is a huge plus for your IP reputation - but that is just half of the work.

When getting answers to your emails, try to keep up the conversations flowing and reply to users who wrote you back.

Having regular conversations is a strong signal for email service providers that your email account is trustworthy - which leads to a quicker warmup of your IP address.

8. Clean your email lists

Regular cleaning of your email lists will help you save your resources as well as keep your open rates and CTRs high - since you will be keeping only email addresses that are used by real people.

Cleaning your email lists can also help you get rid of the users who simply are not interested in your content anymore (and probably won't read your messages even after 5 or 10 email campaigns).

To get rid of invalid email addresses, spam traps, or soft bounces, you need to use tools like EmailListVerify that can automatically “catch” and delete these types of addresses for you.

Regular checking and cleaning of your email lists can help you to:

  • Save money (and time) - with a “healthy” email list, you can be sure that your emails are delivered to real people and not wasted on error email addresses or bots.

  • Protect your IP reputation - every email list can get some invalid email address, soft/hard bounces, or spambot from time to time. That's why regular verification of emails in your list can protect your IP and domain reputation and keep them safe from unwanted email addresses

9. Use warm up tool

Warming up a new IP is a pretty straightforward process but also very time-consuming: you have to prepare engaging content, keep up with conversations, and continuously send more and more emails over a long period of time.

That is why it is always a good idea to use tools that are capable of warming up inboxes for you, such as our Warmup Inbox tool.

Benefits of using an Email Warming Service

Warmup Inbox is a pretty easy and straightforward tool - it sends out emails on your behalf, gets responses, creates engagement in email threads, etc. within our platform.

It contains hundreds of other email accounts that automatically communicate with each other.

Once your email account is synced with Warmup Inbox, there are a number of ways that our tool can help automate the process of building up your email reputation:

  • Send and receive automatic emails - Warmup Inbox is capable of creating dynamic content that is sent and received within our platform

  • Pull out your emails from the spam folder - if some of your emails end up marked as spam by an ESP, Warmup Inbox will automatically pull those emails out from the spam folder and correct them as important messages (which will automatically improve the reputation of your email account)

  • Monitor email blacklists - Warmup Inbox monitors all major email blacklists and constantly checks if any of the synched email accounts are not listed in some of them.

  • Track your “health” score - Warmup Inbox tool will give you a clear overview of the sender health of your sender domain - it scores your account on a scale of 0 - 10 based on many factors that influence the email deliverability (e.g.blacklists, security protocols, the quality of your email message, etc.)

Tip: If you are preparing a wide-scale email campaign, you can book a 30-minute free consultation.


Start landing in more inboxes. 
Use Warmup Inbox to improve your sender reputation and increase your deliverability.

No credit card needed!

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