Best Email Warmup Tools 2025: Complete Comparison

Why You Need an Email Warmup Tool

Let me paint you a picture. You’ve just set up a brand new email account, maybe you bought a fresh domain too. You’re excited about your cold email campaign. You load up your prospect list, craft the perfect message, and hit send to 500 people on day one.

Within hours, your emails are in spam. Your domain gets flagged. Gmail and Outlook have already decided you’re a spammer before you even got started.

That’s the harsh reality of cold email in 2025. New email accounts have zero reputation. To the email gods at Google and Microsoft, you’re guilty until proven innocent. If you start sending cold emails immediately without warming up your account, spam filters will destroy you.

This is exactly where email warmup tools come in. They build your sender reputation before you start your outreach, so your cold emails actually land in the inbox instead of the digital trash can.

Here’s what a good warmup tool does for you. It sends emails from your account to a network of real accounts controlled by other users of the platform. Those accounts open your warmup emails, reply to some of them, and most importantly, move any emails that land in spam back to the inbox. This spam rescue feature alone is worth the price of admission.

All of this generates positive engagement signals that Gmail, Outlook, and other providers use to determine whether you’re a legitimate sender. Opens tell them people want your emails. Replies prove you’re having real conversations. Not-spam actions confirm you’re trustworthy. Over time, usually about two to three weeks, your account builds enough reputation to start sending cold emails with good deliverability.

The result is simple but powerful. Your cold emails actually reach the inbox instead of spam, and your outreach campaigns actually work.

How Email Warmup Actually Works Behind the Scenes

The concept is clever when you break it down. Warmup tools create a network of thousands of users who are all warming up their accounts together. When you connect your inbox to a warmup tool, you’re joining this network.

Your account starts sending warmup emails to other accounts in the network. These emails get routed to people who are also warming up their accounts. When they receive your warmup email, their warmup tool automatically opens it, and maybe replies to it. If your email landed in their spam folder, the tool moves it to the inbox and marks it as not spam.

At the same time, you’re receiving warmup emails from other people in the network, and your warmup tool is doing the same thing on your end. Opening their emails, replying to some, rescuing them from spam. It’s a mutual benefit system where everyone helps everyone else build reputation.

The best warmup tools make all of this completely automatic. You don’t send a single email manually. You don’t open anything yourself. The tool handles everything, sending emails at random intervals throughout the day, varying the content so it looks natural, and generating engagement that looks real to email providers.

This works because email providers are watching everything. They track how many of your emails get opened, how many get replies, how often people mark you as spam, and how often people move you out of spam. When warmup tools manufacture positive signals at scale, your reputation improves. When your reputation is strong enough, your actual cold emails get through.

Top Email Warmup Tools Compared

Let’s cut to the chase. Here’s how the major players stack up against each other.

Now let’s get into the details of each one.

Instantly: The All-in-One Powerhouse

Instantly has become the go-to choice for teams who want everything in one place. You get email warmup combined with cold email sending, unlimited email accounts, and a unified inbox for managing all your replies.

Pricing is straightforward. The Growth plan is $37 per month and includes unlimited warmup for as many email accounts as you want, plus 5,000 leads in your database. The Hypergrowth plan at $97 per month removes all limits completely. There’s also a Light plan at $30 per month if you’re just testing things out.

The warmup feature itself is solid. Instantly sends warmup emails automatically on a smart schedule that mimics real human behavior. The spam rescue feature constantly monitors your emails and moves them from spam to inbox when needed. You get a deliverability dashboard that shows exactly how your reputation is building over time.

But the real power of Instantly is how warmup integrates with sending. You can rotate your cold emails across multiple warmed-up accounts, which spreads your sending volume and protects your reputation. When replies come in, they all flow into one unified inbox, so you’re not juggling multiple accounts.

The downside is that you’re locked into using Instantly for sending. You can’t just use it for warmup and send from another tool. For some teams, that’s fine. For others who are already committed to a different sending platform, it’s a dealbreaker.

The interface is clean and intuitive, and the team ships new features regularly. If you’re starting fresh with cold email and want one platform that handles everything, Instantly is your best bet.

Lemwarm: The Dedicated Warmup Specialist

Lemwarm comes from the team behind Lemlist, but it works as a standalone warmup tool that integrates with any email platform you’re using. This makes it perfect for teams who already have a sending tool they love and just need reliable warmup.

The network is impressive at over 20,000 email accounts, which means your warmup emails are getting distributed to a large, diverse pool. More importantly, these accounts are actively maintained and controlled by real users, not just fake accounts sitting idle.

Pricing is per inbox. The Essential plan is $29 per month for one inbox, and the Smart plan is $49 per month with additional features. If you’re warming up five or ten inboxes, the cost adds up quickly compared to Instantly’s unlimited approach.

Features include everything you need. Automatic warmup scheduling, spam rescue, deliverability score tracking, and reputation monitoring. You can customize your warmup settings if you want more control, though the defaults work well for most people.

The reporting is detailed without being overwhelming. You can see exactly how many warmup emails are being sent, what your open rates look like, and whether emails are landing in spam. This transparency helps you understand when your account is ready for cold outreach.

The main limitation is that Lemwarm only does warmup. No sending features, no unified inbox, no campaign management. You need to bring your own sending tool. If you’re already using something like Mailshake, Woodpecker, or even just manual Gmail campaigns, Lemwarm slots right in.

For teams committed to another platform who need proven, reliable warmup, Lemwarm delivers.

Warmbox: The Budget-Friendly Choice

Warmbox is the option for people who want solid warmup without breaking the bank. At $15 per month for a single inbox, it’s literally half the price of Lemwarm and less than half of Instantly.

Despite the low price, you’re getting a large network of over 35,000 email accounts. That’s actually bigger than Lemwarm’s network. The auto-warmup works well, spam rescue is included, and you get deliverability monitoring to track your progress.

Warmbox also includes a DNS health checker, which verifies that your SPF, DKIM, and DMARC records are set up correctly. This is surprisingly useful for catching technical issues that could hurt your deliverability before you even start sending.

The Solo plan at $15 per month covers one inbox. The Start-up plan at $69 per month handles three inboxes. The Growth plan at $139 per month manages six inboxes. The pricing scales reasonably well if you need multiple accounts warmed up.

Where Warmbox shows its budget roots is in the interface and support. The UI is functional but not as polished as Instantly or Lemwarm. The team is smaller, so support can be slower. Advanced features that competitors offer might be missing or less refined.

But here’s the thing. If you’re a solo founder testing cold email, or a small team watching every dollar, Warmbox gets the job done. Your emails still get warmed up, your reputation still builds, and you save money for other parts of your business.

Mailwarm: The Enterprise Play

Mailwarm positions itself as the premium, enterprise-grade option. The Starter plan is $79 per month for one inbox, which is already more expensive than any other option we’ve covered. The Scale plan hits $479 per month for ten inboxes.

What do you get for that premium? Priority support, API access for custom integrations, a dedicated account manager on higher tiers, and highly customizable warmup settings. The platform is built for enterprise teams with specific compliance needs or complex technical requirements.

The network is actually smaller than competitors at around 1,000 accounts. That’s not necessarily bad since Mailwarm claims these are higher-quality accounts, but it’s worth noting.

For most teams, Mailwarm is overkill. Unless you have enterprise-specific needs that justify the premium pricing, you’re better off with Instantly or Lemwarm. The features don’t justify the 2-5x price increase for typical cold email use cases.

Lemlist: The Personalization Platform

Lemlist is technically an all-in-one platform like Instantly, but it’s really built for teams who want advanced personalization in their outreach. Think custom images with your prospect’s company logo, embedded videos, multichannel sequences that combine email and LinkedIn, and A/B testing for every element.

Warmup is built into Lemlist using their Lemwarm technology. The Email Starter plan at $59 per month includes basic warmup and sending. The Email Pro plan at $99 per month adds more advanced features.

If personalization is your game and you’re running sophisticated campaigns, Lemlist makes sense. But if you’re doing straightforward cold email without a lot of customization, you’re paying for features you don’t need. Instantly offers better value for pure cold email.

Smartlead: The Rising Challenger

Smartlead is the newer player that’s gaining traction quickly. At $39 per month for the Basic plan, it slots in between Instantly and Lemlist on pricing while offering unlimited warmup, email rotation, and a master inbox for managing replies.

The platform is actively developed with new features shipping regularly. The interface is modern and clean. They’re building API access and white-label options for agencies.

The catch is that Smartlead is less proven than Instantly or Lemwarm. The warmup network is smaller and still growing. Some features feel like they’re still maturing compared to established competitors.

If you’re willing to try a newer platform for good value, Smartlead is worth considering. Just know you’re taking a bit more risk than going with the established players.

How to Choose the Right Warmup Tool

Here’s my framework for making this decision quickly.

Choose Instantly if you want one platform for warmup and sending, you’re starting fresh with cold email, deliverability is your top priority, and your budget is around $40 to $100 per month. This is the best all-around choice for most teams.

Choose Lemwarm if you already use a sending tool you love, you just need standalone warmup, you want proven reliability, and your budget is $30 per month per inbox. This is the best specialist tool.

Choose Warmbox if budget is your primary concern, you’re testing cold email for the first time, you need basic warmup that works, and your budget is $15 to $70 per month. This is the best value play.

Choose Lemlist if personalization is critical to your campaigns, you want image and video in emails, you need multichannel outreach combining email and LinkedIn, and your budget is $60 to $100 per month.

What Separates Good Warmup Tools from Bad Ones

After testing every major warmup tool across hundreds of client accounts, here’s what actually matters.

Auto-warmup is non-negotiable. The tool must send and receive warmup emails without any manual work from you. If you’re manually doing anything, it’s not a real warmup tool.

Spam rescue is critical. The tool needs to automatically move emails from the spam folder to the inbox and mark them as not spam. This feature alone creates massive reputation improvements.

Network size matters, but bigger isn’t always better. You want at least 10,000 accounts in the network, but 50,000 low-quality accounts are worse than 10,000 high-quality ones. Look for networks with active, real users.

Open and reply simulation should happen automatically. The tool needs to create engagement signals that look natural to email providers, with varied timing and realistic behavior.

Progress tracking helps you know when you’re ready to send. Good tools show warmup status, deliverability scores, and reputation metrics so you’re not flying blind.

Nice-to-have features include DNS health checking, custom scheduling, multi-inbox management, and integration with your sending tools. These aren’t required but they make life easier.

Red flags to watch out for: very small networks under 5,000 accounts, no spam rescue feature, manual warmup steps required, no reputation monitoring, and suspiciously cheap pricing like free or under $10 per month. If something seems too good to be true, it usually is.

Setting Up Your Warmup Tool the Right Way

Once you’ve chosen a tool, setup matters. Connect your inbox using IMAP and SMTP credentials or OAuth if the tool supports it. Start conservative with just 10 to 20 warmup emails per day for the first few days.

Enable spam rescue immediately. This is the feature that does most of the heavy lifting. Set your warmup to run during business hours so the activity matches when you’ll actually be sending cold emails. Configure a reply rate between 30 and 50 percent, which looks natural.

For the first week, check your warmup dashboard daily. Look for emails moving from spam to inbox. Verify that open rates are high, ideally 80 percent or better. As your reputation builds, you can gradually increase the volume.

The biggest mistake people make is stopping warmup too early. You need to keep warmup running forever, even after you start cold outreach. A good rule of thumb is to maintain warmup at 20 to 30 percent of your total email volume. If you’re sending 100 cold emails per day, keep 20 to 30 warmup emails running alongside them.

Other common mistakes include setting volume too high too fast, ignoring the metrics in your dashboard, and trying to use multiple warmup tools on the same inbox. Stick to one tool per inbox and let it do its job.

Key Takeaways

Email warmup isn’t optional if you want your cold emails to actually work. The right tool depends on your specific situation, but here’s what you need to know.

Instantly is the best choice for all-in-one warmup and cold email sending. If you want everything in one platform, start here.

Lemwarm is the best standalone warmup tool with a network of over 20,000 accounts. If you already have a sending tool you love, this is your warmup solution.

Warmbox offers the best value for budget-conscious senders. If you’re watching every dollar, you can still get solid warmup for half the price of competitors.

Look for these features in any warmup tool: automatic warmup, spam rescue, a large network, and good integration options. Expect to pay between $15 and $50 per month per inbox for quality warmup.

Most importantly, keep warmup running continuously. It’s not a one-time setup. It’s an ongoing investment in your sender reputation that pays dividends every time your cold emails land in the inbox instead of spam.

Need Help Choosing?

We’ve tested all major warmup tools across hundreds of client accounts. If you’re not sure which is right for you, book a call and we’ll recommend the best setup for your situation.