If your cold emails are landing in spam, the problem isn’t always your copy or your offer, it’s usually your reputation. And that’s exactly what an email warm-up tool helps fix.
But not all warm-up tools are created equal. Some can actually hurt your deliverability more than they help. Here’s how to pick the right one.
An email warm-up tool helps new or cold mailboxes build reputation with inbox providers like Gmail, Outlook, Yahoo, and Microsoft.
It works by automating realistic mailbox activity: sending, receiving, opening, replying, and even pulling emails out of spam. Over time, this activity signals to mailbox providers that you’re a trustworthy sender, making it more likely your real outreach lands in the inbox.
At Mailivery, we define email warm-up as:
“Automated, human-like email engagement that mimics natural inbox behavior to build trust with mailbox providers and improve inbox placement.”
The point isn’t just sending test emails. It’s about training the email ecosystem to recognize your account as safe and reliable.
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For more info, check out our What is Email Warm Up Explained guide.
Now, let's dive into what you need when picking an email warm-up tool
Warming up an email account only works if your messages are exchanged across a large, diverse network of inboxes.
Look for a tool that covers Google, Microsoft, Yahoo, Outlook, Gmail, and other providers. A narrow pool (say, just Gmail) doesn’t train inbox providers effectively because your sending reputation has to be built across ecosystems.
If a tool boasts “thousands of inboxes,” dig deeper. Are they real mailboxes on major providers, or cheap throwaway domains that don’t teach providers anything useful?
Some platforms advertise AI agents, headless browsers, or simulated mouse movements to make warm-up look “human.”
Here’s the problem: inbox providers don’t care how advanced the simulation looks. They care about how real mailboxes behave.
Browser automation often leaves fingerprints (like identical session patterns or bot-like timing) that actually flag you as suspicious. And once providers detect that behavior, your emails are at risk of being filtered harder.
A proper warm-up network should be based on authentic mailbox interactions, not scripts trying to trick Gmail into thinking they’re people.
To understand more about network safety and protecting your reputation, read Top Email Blacklists That Wreck Cold Outreach.
Every sender has different goals. A good warm-up tool should let you control the pace and patterns of your warm-up:
Without customization, you’re stuck with a generic process that may not match your actual sending needs.
The reality: some users will mark warm-up emails as spam. If a provider doesn’t have safeguards, that can drag down the entire network.
At Mailivery, we use a two-strike system. If someone marks warm-up emails as spam twice, they’re removed from the network. That way, bad actors don’t poison the pool.
When you evaluate a tool, ask: “What’s your policy for users who abuse the network?” If they don’t have a clear answer, move on.
If you want to understand more about why emails end up in spam folders, check our article Why Your Emails Are Going to Spam.
A lot of cold email tools tack on “warm-up” as a feature, think Instantly, Smartlead, Lemlist.
The issue? Their main product is sending, not warming. Warm-up becomes a side module with limited mailbox diversity, weaker safeguards, and less focus on reputation-building.
You’ll get better results from a tool built specifically for warm-up and deliverability, not one that treats it as an add-on.
Some tools charge you per inbox you warm up. That might sound fair until you’re scaling and realize you’re paying 10x more just to protect client accounts.
Instead, look for a tool that offers unlimited inbox warm-up for a flat price. This is far more cost-effective, especially for agencies managing multiple accounts.
A good warm-up tool shouldn’t stop at sending fake emails. Deliverability is bigger than that.
Look for features like:
The right platform grows with you beyond warm-up.
If you’re an agency or SaaS company, APIs matter. You want the ability to:
Many “all-in-one” tools don’t offer much here. A warm-up tool with robust API coverage is the smarter choice if scalability and integration are on your roadmap.
The right warm-up tool isn’t just about sending fake emails, it’s about building long-term trust with inbox providers.
Focus on:
Pair these with Email Deliverability Best Practices to ensure your campaigns consistently land in the inbox.
If you choose wisely, you’ll have a tool that not only fixes today’s inbox issues but also keeps your cold email strategy future-proof.
Ready to start warming up safely? Mailivery gives you unlimited inbox warm-up, a 50,000+ mailbox network, and deliverability features built for agencies and SaaS teams. Try Mailivery today.
The easiest way to get responses to your cold emails.
