Does Email Warm Up Work & Is It Necessary?

Are you wondering if you should warm up your inboxes before sending cold emails?

Warm-up has become an expected feature on almost every cold email platform, so it's a fair question. But "warm-up" has quietly come to mean two very different things, and the difference is everything.

One kind is artificial warm-up: tools that add your account to a pool of other accounts that all email each other and fake replies, opens and "important" markers to manufacture a high response rate. This is the kind I've argued against for years — at best it does nothing, at worst it could get your emails marked as spam by email service providers.

The other kind is measurement-based warm-up: using real seed inboxes to actually measure where your emails land (inbox vs. spam) and ramping your sending volume gradually and safely. This one is legitimate, and it's the approach we're building at Emailchaser with our Warm-Up Pool.

I’ve been sending cold emails for many years, and have also built a leading cold email software (Emailchaser), so I am qualified to talk on this subject.

In this article, I will cover the following:

- What is email warm up?
- Does artificial email warm up work?
- Are artificial email warm up tools safe to use?
- Traditional warm-up vs. measuring real inbox placement
- Is email warm up necessary?

What is email warm up?

Email warm up, also known as email warming, is the process of gradually increasing the number of emails that you send from a new email account.

The reason why some people think that email warm up is a good idea is because most email service providers will think that a sudden increase in email volume from a new email account is suspicious, causing your emails to go to the spam folder.

If you create a new email account, and you immediately send hundreds of emails, then your emails will go to spam.

The idea of email warming is to gradually increase the number of emails being sent from your new email account. If you send your cold emails with Emailchaser, then this gradual build-up will happen by default.

So far, so sensible — a gradual ramp is a genuinely good idea. The problem is with what most warm-up tools bolt on top of the ramp. They don't just gradually build up your sending volume. They also try to artificially manipulate your response rate by adding your email account to a warm-up pool with other email accounts, and then all of these email accounts are used to respond to each other.

The idea is that this will improve your deliverability because email service providers will see that you have a high response rate.

The problem with this is that it's very obvious when an email account is part of an artificial warm-up pool.

Leading email service providers, such as Google and Microsoft, have advanced algorithms that can easily detect this. This means that right out of the gate, you've made it known to Google and Microsoft that you're trying to manipulate your response rate, and they will blacklist your email accounts.

Even the co-founder of Instantly (email warm-up software) admits at 15:07 in the below video that they used an external warm-up API to build their email warm-up feature. This implies that their warm-up feature is not advanced, and is something anyone could put together, meaning that Google and Microsoft will be able to detect these warm-up emails easily:

Does artificial email warm up work?

The short answer is no — not the artificial, fake-engagement kind.

Trying to artificially manipulate your response rate with email warm-up tools is not effective, and will cause your emails to go to spam as email service providers will blacklist your email accounts and domains.

Many companies offer email warm-up tools which add your email accounts to a warm-up pool. All promising “improved deliverability”, while providing zero evidence of any results.

At 05:31 in the below video, the founder of an email deliverability company called Folderly states that email warm up tools do NOT work:

The below video shows data on how popular email warm up tools decrease your reply rate (compared to using no warming):

There are many factors that affect email deliverability, and the idea that email warm up is the "silver bullet" of cold email deliverability is a myth perpetuated by companies that sell email warm up services. If you want to learn how to guarantee the best possible deliverability, then I recommend that you read my article 13 Ways To Prevent Your Cold Emails From Going To Spam.

Even if these warm up tools were effective, the question of whether they will remain effective long term is debatable since email service providers such as Gmail do not allow the use of them. Fake-engagement warm up tools are against Gmail’s terms of service.

Google has the world’s most advanced algorithms and AI. Do you really think they don’t know when email accounts in email warm up pools are sending fake emails to each other to manipulate response rates?

Companies that offer email warm up features often point to the number of email accounts in their warm up pool, as if this somehow means that Google and Microsoft can't detect the warm up pool due to the volume of accounts.

The reality is that it is still extremely easy for Google and Microsoft to detect emails from these warm up pools, since the type of email accounts found in them are not representative of the average email account that exists in the real world. For example, virtually all email accounts found in these pools will be brand new, and from either Google or Microsoft; it is not difficult to detect when an email account is part of a warm up pool when all of the emails being received are from email accounts that are not even remotely representative of the general population.

Fake-engagement email warm up tools are not effective, and the only people promoting them are financially incentivized to sell you them.

The below LinkedIn post shows how Erol Toker's email accounts were burnt (blacklisted) immediately when he used an email warm up tool:

The below Tweet shows that these warm up tools decrease your response rate:

Turn off warmup?

Tested lots with cold email over past 8 weeks

Our reply rates improved when not using warm up

Guys in my group have tested this too and seen similar results

Spoke to smarter guys than me who have also seen similar results

Might be worth testing

— Sean (@seanb2b) July 5, 2024

Are artificial email warm up tools safe to use?

Fake-engagement email warm up tools are not safe to use.

Email service providers such as Gmail don’t allow them and will blacklist your email address if you use them. It is against Google’s terms of service to use these tools.

The below tweet shows a statement from Google explicitly stating that email warm up tools are not allowed, and if used, will cause your emails to be marked as spam:

Whoa, just got this notice from Google.

Is this THE END of email warmup services?

Anybody else offering warmup get this? pic.twitter.com/TIMeMLfw3H

— Ajay Goel (@PartTimeSnob) November 16, 2022

Google goes even further, as shown in the below tweet:

Google is even more autocratic about the email warmup takedown than I expected. After informing them I've disabled the service, they sent me this.

I'm not even allowed to MENTION warmup of Google accounts anywhere on my site. pic.twitter.com/JUuyiVuLa0

— Ajay Goel (@PartTimeSnob) February 8, 2023

Even the founder of Gmass (popular email warm up tool) admits that email warm up is not safe and has shut down his entire warm up tool:

That's a wrap.

After sending 1,295,152,830 warm-up emails for 236,084 email accounts over two years, the GMass warm-up service is over.

All warm-up functions have ceased except the auto-archiver. I'll let that run for a few more hours.

So now what?

— Ajay Goel (@PartTimeSnob) February 1, 2023

To summarize, Google (Gmail) and other email service providers are clamping down hard on fake-engagement warm up tools. These are the most advanced companies in the world, and they can easily identify fake emails sent from email warm up pools. I recommend that you don’t use any warm up tool that manufactures fake engagement, as your emails will likely be marked as spam if you use them.

Additionally, it's possible that there are "spam traps" distributed inside of popular email warm-up pools, meaning that if you add your email accounts to those email warm-up pools, then your emails may be marked as spam. Think about it logically, if you were an email service provider trying to catch all of the people that are manipulating response rates, then adding spam traps to these warm-up pools would be an easy way of doing so.

Finally, one of the main factors affecting your deliverability is your total sending volume. Fake-engagement warm up tools contribute to your overall sending volume, which isn't a good thing. If you don't understand why your sending volume matters, then I recommend that you read my article How Many Cold Emails Can You Send Per Day Before Going To Spam?

The below video at 34:09 shows someone getting 86 email accounts blocked by Google when they used Smartlead's warm up tool for 2 weeks:

Traditional warm-up vs. measuring real inbox placement

Everything above is about artificial warm-up — pools of brand-new, disposable accounts faking engagement to manipulate your reply rate. That approach is detectable, ineffective, and against the rules.

But there is a completely different, legitimate practice that also gets called "warm-up", and it's worth separating from the fake-engagement kind: measuring where your emails actually land.

Instead of faking a reply rate and hoping for the best, you send to a network of real seed inboxes across the major providers (Gmail, Outlook, and others) and check whether each message lands in the inbox, the spam folder, or a promotions tab. That gives you a real, measurable inbox-placement score — not a vanity metric you can't see or verify.

The differences that matter:

- Real inboxes, not bots. The seed network is made up of real, representative inboxes that receive and interact with your mail the way a real recipient would — not a swarm of brand-new accounts that only ever talk to each other.
- Measurement, not manipulation. The goal isn't to trick a spam filter into thinking you're popular. It's to tell you where you actually land, so you can fix the underlying problem (authentication, content, sending volume, or list quality).
- A gradual ramp on a safe budget. Volume increases gradually and counts against the same safe daily limit your real campaigns use, so you never overshoot what a mailbox can handle.
- No tracking pixels. Legitimate warm-up never adds open-tracking pixels to your emails, which can hurt your deliverability on their own (see Does Open Tracking Hurt Deliverability?).

This is the distinction we're building Emailchaser's Warm-Up Pool around: real seed inboxes and a placement (or "heat") score that tells you where your emails are actually landing — rather than a fake reply rate you can't trust. Warm-up has become an expected feature across cold email platforms, and this measurement-first version is the honest one.

The takeaway isn't "all warm-up is a scam." It's that you should be deeply sceptical of any tool selling you a manufactured reply rate, and you should care a lot about tools that measure your real inbox placement.

Is email warm up necessary?

The honest answer: artificial, fake-engagement warm up isn't necessary — but knowing where your emails actually land is.

I still recommend that you don’t use an artificial warm-up tool that fakes engagement, because there is no evidence showing these tools work, and plenty showing they can get your accounts burned. If you use one, the best case scenario is that it has no effect; the worst case scenario is all of your emails being marked as spam by email service providers.

At 30:00 in the below video, Jesse Ouellette discusses how his company is now launching cold email campaigns without using (artificial) email warm-up tools:

That said, "don't fake it" is not the same as "fly blind". Two things genuinely help:

- Ramp gradually. Don't blast hundreds of emails from a brand-new mailbox on day one — build the volume up over time. (Emailchaser does this by default.)
- Measure your placement. Use real seed inboxes to see whether you're actually hitting the inbox, so you can catch and fix a deliverability problem before it burns your domain.

And the single biggest lever is still list quality. The best way to avoid spam folders is by only contacting people that actually need your product or service. You can learn how to do this in my article How To Create An Evergreen Cold Email Campaign.

The below video shows a conversation that discusses why artificial email warm up tools aren't effective:

Artificial warm up reminds me of Private Blog Networks (PBNs) in SEO. I’ve been doing SEO for nearly a decade, and when I first got started, a lot of people who were selling SEO courses were teaching the use of PBNs to build backlinks to websites. This method was spam (just like how fake-engagement warm up is spam), and doesn’t work, isn’t long term sustainable, and is easily detectable by Google.

Now, I would never use PBNs as I know how to build quality backlinks from real authoritative websites. The same applies to cold email — I would never use a fake-engagement warm up tool knowing what I know now. But just as real analytics and real backlinks are worth having, measuring your real inbox placement is worth having. The difference is always the same: manufacture a fake signal, or measure and improve the real one.

Even today, you can go to Fiverr and buy 5,000 spammy backlinks from someone. Just because the service is offered, doesn’t mean it is effective or safe. Just because there are people willing to sell you fake-engagement warming tools, doesn’t mean that they work, are safe or that you should use them.

Final thoughts

Email warm up tools that attempt to artificially manipulate your response rate by adding your email accounts to a pool of fake-engagement accounts are not effective. These warming services are also unsafe, as they are banned by email service providers such as Google and Microsoft, who will mark your emails as spam if you use them.

But "warm-up" now covers more than that. Ramping your sending volume gradually, and using real seed inboxes to measure whether you're landing in the inbox or spam, is a legitimate and measurable practice — and it's the approach we're taking with the Emailchaser Warm-Up Pool.

There is no "silver bullet" for deliverability. The best way to stay out of the spam folder is still to only contact people that actually need your product or service (see How To Create An Evergreen Cold Email Campaign), and to measure your real inbox placement so you can fix problems early instead of guessing.