10 best email warmup tools and practices in 2025

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Email warmup is a critical process if you’re launching an email marketing campaign from a new domain or account. 

It involves gradually increasing the volume of sent emails over time to establish a positive sender reputation with internet service providers (ISPs) and email service providers (ESPs).

Without an effective email warmup tool, a sudden surge in email activity from a fresh domain can trigger spam filters and risk your messages going to junk folders or even getting blocked completely. With an email warmup plan, you can significantly improve your email delivery rates and ensure you reach your recipients’ inboxes.

This guide explores the best practices to warm up an email domain with insights on how you can prepare your email warmup for successful campaigns. We also provide a step-by-step guide on warming up your email domain using Omnisend’s email automation tools so you have a solid foundation for your email marketing efforts.

Email domain warmup explained

Email domain warmup is the process of progressively sending test emails from a freshly-made domain. This establishes a positive sender reputation before launching full-scale email campaigns. 

The key reason to warm up your email domain is to increase email deliverability. You need to earn the trust of ISPs and ESPs by improving your sender reputation.

If you plan to send a high volume of emails, then email domain warming is essential because your audience’s ESPs (and your recipients) are more likely to flag messages from the new domain and send them straight to the “Spam” folder. In fact, 43% of email recipients flag messages as spam, making a warmup email strategy all the more important.

ESPs also impose stringent sending limits that restrict your ability to send high volumes of cold emails, potentially affecting deliverability. This is why email warmup is so vital to your new domain’s chances of succeeding.

As recipients respond positively to your emails, the ISPs begin to trust your domain. The ESPs will gradually increase your sending limits, improving your email deliverability, which can be influenced by several factors:

• Sender reputation: This quality score is everything, as ESPs assign it based on your sending history. As a new email domain, you’ll need to build up your sender reputation to boost deliverability.
• Delete rate: This measures how often recipients move your emails to their trash folder without reading them. A high delete rate can negatively impact your reputation.
• Spam reports: When recipients mark your emails as spam, it sends a spam report. This signals to ISPs and ESPs that your content may be unwanted.
• Unsubscribe requests: These are less harmful than spam reports but will still indicate a lack of interest in your messages. It can affect your reputation if rates climb too high.
• Email content quality: Things like spam trigger words, grammatical errors, and suspicious links tarnish email content quality. These can all lower your reputation score.
• Engagement rate: This is a positive metric that measures how often recipients interact with your emails through opens, replies, and forwards. Higher engagement typically improves reputation.
• Blacklisting: Presence on email blacklists can severely damage your reputation. Even being listed on a minor blacklist can have consequences.
• Email bounce rate: A high bounce rate indicates the proportion of emails that fail to deliver. This can suggest poor subscriber list quality or email sending practices.

Other factors like sending consistency, authentication protocols, and following best practices also influence overall domain and email sender reputation. This makes email domain warmup essential for establishing a good email sender reputation.

In fact, it is vital for overall email marketing success. Email domain warmup improves inbox placement, open rates, click-through rates, and conversions.

Email warmup tools: Why you should avoid them

Given the importance of warming your email domain, it’s no surprise that there are numerous companies offering to do it on your behalf. 

But for the most part, you shouldn’t use them.

There are a couple of reasons for this. First, the process is straightforward and most email service providers, including Omnisend, have features to help you through the warmup phase. It’s as simple as following best practices and having a little patience.

The second reason is that these email warmup tools often cross the line of best practices, and they’re widely used by spammers. The services offered by these platforms can vary, but you may find the  following:

• Audience lists provided to you: this means recipients didn’t consent to hear from you
• Optimizing an audience for cold outreach: cold outreach isn’t always spam, but in most cases it is and can therefore breach regulations like GDPR
• Reputation rebuilding: often done by sending emails to fake addresses, then simulating positive engagement on the other end to pretend that real recipients are receiving legitimate emails

As you can see, these email warmup tools go against best practices and may backfire completely, leading to worse deliverability or even your domain being blacklisted.

Instead, the best practices are to send legitimate emails to your subscribers, starting with a low volume and gradually increasing how many you send. If you use Omnisend’s warmup feature, we’ll split your emails through our shared sending domain, to prevent your customer domain sending too much too early. This helps you build trust with mailbox providers, and you can safely send larger volumes of emails to your audience.

Warm up email domain with Omnisend

Omnisend offers one of the most streamlined solutions to systematically warm up email domains. To warm up your email domain with Omnisend, follow the steps outlined below or use our video tutorial:

• Prepare for warmup: Before you begin your email warmup sequence, thoroughly declutter your email lists. Ensure your email content is of high quality as well. Implementing this strategy guarantees maximum engagement throughout the earliest stages. 
• Get started with Omnisend: To get started, create an account with Omnisend. If you have data from a previous marketing automation platform, you can migrate it into Omnisend. This helps you retain your existing customers’ information. 
• Segment your email list: Split your email list into small groups based on activity levels. Segment contacts into two groups: most active and engaged contacts. It’s important to note that Omnisend automatically creates different segments the moment you subscribe or connect your store to its platform.
• Initiate the warmup with Omnisend: Once in your dashboard, select Store settings → Email → Sender domains → Domain setup → Pick the custom domain for your campaigns. The warmup duration could take several further steps, depending on your subscriber volumes.

• Email campaigns during warmup: Use or create distinct content for each new warmup batch. This helps you avoid repetitive sends because contacts may overlap across segments. Omnisend also automatically generates segments for your warmup campaigns.
• Monitor and fine-tune your email warmup strategy: Closely track important email marketing metrics. This includes open, clickthrough, and engagement rates to gauge ISP response. Low engagement signals slower expansion, so monitor and adjust if necessary.

Best practices to warm up an email domain

• Create a warmup strategy
• Segment your email list
• Clean your email lists
• Follow ESP limits
• Start with a low volume
• Target engaged recipients first
• Authenticate your email
• Improve IP reputation
• Avoid spam triggers
• Craft high-quality content

Email domain warming is best approached as a science, not an art. This means that it is not an exercise that you freestyle. Rather, it’s a well-organized process.

This includes starting with a small volume so ESPs don’t consider you a spam threat as you establish your reputation. It also includes responding promptly to feedback, and segmenting your audience appropriately to ensure everyone receives relevant, appropriate information.

That said, here are some best practices for email domain warming:

Create a warmup strategy

Develop a well-thought-out email warmup strategy before launching an email marketing campaign from a new domain.

Consider the following when creating your email warmup strategy:

• Your high-performance emails: Put your best-performing emails forward. This will increase the chances of good engagement, which tells ESPs that you’re sending high-quality messages.
• Your engaged audiences: Create an email list of recipients most likely to open and interact with your emails. This improves your sender reputation as it shows that your recipients are engaging with you.
• A timeline: Create a schedule that details how many emails you’ll send per day or week. Also, detail how you plan to increase the volume and frequency of emails over time. We recommend you send no more than one campaign per day, three times a week.

A warmup strategy could look something like this:

Week	Emails/day	Emails/week	Segmented audience
Week 1	250 emails	750 emails	Existing subscribers only
Week 2	500 emails	1,500 emails	Existing subscribers + most active customers
Week 3	1,000 emails	3,000 emails	Existing subscribers + all customers
Week 4	2,000 emails	6,000 emails	Existing subscribers + customers + new signups

You can monitor your email marketing data after a few weeks and start to increase the number of emails you send.

Segment your email list

By segmenting your email list, you can optimize your domain warmup campaigns. Using personalization and targeting to segment your list can improve your email deliverability and performance.

For instance, Omnisend’s segmentation feature involves splitting your email list into specific groups based on shared characteristics, such as:

• Preferences
• Geographics
• Demographics
• Purchase history
• Customer behavior
• Engagement levels
• Active/inactive subscribers

Clean your email lists

Regularly remove inactive or invalid email addresses from your email list.

Regular email list cleaning and updating can significantly improve your email deliverability. It enables your messages to reach only engaged and interested recipients.

Use email verification or cleanup tools to identify and remove spam traps, hard bounces, and other problematic email addresses from your list.

Follow ESP limits

When following an email warming strategy, it’s essential to identify the limits imposed by ESPs. You must adhere to these sending limits to avoid being marked for suspicious activity or added to the spam list.

This table shows some of the sending limits of some popular ESPs in 2025:

ESP	Limit
1and1	50-500 emails/hour
BlueHost	150 emails/hour
DomainFactory	50-10,000 emails/hour
DreamHost	100 emails/hour
FrogHost	1,000 emails/hour
Gmail	500 emails/day
GoDaddy	500-1,000 emails/day
Google Workspace	2,000 emails/day
HostGator	500 emails/hour
Hostinger	1,000-3,000 emails/day
InMotion	250 emails/hour
Mailchimp	500-7,500 emails/day
Namecheap	50-10,000 emails/hour
Microsoft365	10,000 emails/day
Outlook/Hotmail (free)	300 emails/day
RackSpace	10,000 emails/day
Yahoo!	500 emails/day
Zoho	250-2,500 emails/day

It’s important to note that these limits can change and will frequently vary based on the provider’s plan.

Start with a low volume

When warming up an email domain, it’s advisable to send low-volume emails and gradually scale up. As previously mentioned, this approach helps to build a positive sender reputation. Exceeding the ESP send limits as a new domain strongly indicates “spam” activity and often results in actions such as blocking, blacklisting, or spam folder rerouting.

Engaging in inconsistent email warmups can also upset the ISPs. The most effective email warming involves gradually and consistently increasing the volume of emails you send.   

In the graphs below, you can see how consistency can affect your reputation:

Target engaged recipients first

Target your most engaged recipients first, and then you can gradually expand your outreach in batches. Your initial send list should comprise existing customers, recent subscribers, or website visitors with high on-site activity.

Having demonstrated clear interest, this selective group will help your new domain to build a good reputation. They gain momentum through higher open rates, clickthroughs, and lower complaints.

Authenticate your email

When conducting email warming, ensure that your email domain is properly authenticated. This safeguards it against spoofing or forgery by hackers or fraudsters.

Implementing any of the three main email authentication protocols for an email domain is essential. They are SPF, DKIM, and DMARC:

• SPF (Sender Policy Framework): This allows you to specify which IP addresses are authorized to send emails from your domain
• DKIM (DomainKeys Identified Mail): This allows you to sign your emails with an encrypted digital signature to prove legitimacy
• DMARC (Domain-based Message Authentication, Reporting, and Conformance): This allows you to set policies for how the ESPs and ISPs should handle your emails that fail verification

Improve IP reputation

Email domains and IP reputations are deeply linked. Your associated IP address plays a significant role in email deliverability.

IP addresses associated with your email domain come in two forms:

• Shared IP addresses: These are used by multiple senders and are usually provided by your email service provider. They can be likened to a shared office space where multiple companies use the same office address.
• Dedicated IP addresses: Dedicated IP addresses are single-use. They’re usually purchased by the sender.

Be attentive to the reputation of the IP addresses associated with your email-sending infrastructure. It’s important to improve or change it when necessary.

Avoid spam triggers

Steer clear of spam triggers in your email content during domain warmup. Spam triggers can vary depending on the ESP and ISP in question.

Be wary of spam triggers in the following:

• Your email content:
  • Using overly promotional or exaggerated language, such as “free,” “guaranteed,” or “risk-free”
  • Excessive use of capitalization, punctuation, or symbols, such as “BUY NOW!!!,” “LIMITED TIME OFFER!!!” or “$$$”
  • Using generic or impersonal sender names, such as “noreply,” “admin,” or “support”
    
    Take a look at the spam content from this Gmail account:

• Your email list:
  • Sending emails to unconsenting recipients
  • Sending emails to inactive or dormant email addresses
  • Sending emails to spam traps or honeypots
• Your email frequency:
  • Sending too many emails
  • Sending inconsistent emails
  • Sending emails at irregular or inappropriate times

Craft high-quality content

Another best practice for email domain warming is to create high-quality email content. The quality of your email content determines how your recipients perceive and respond to your emails. As such, you want it to impress and convert.

To ensure a successful email domain warming, your email content should be:

• Personalized
• Engaging
• Relevant
• Clear

Take a look at Medium’s newsletter, for example. It’s quite plain. However, the focus isn’t on the design but on the content, which provides value and information recipients are interested in: