The short answer: GMass no longer offers a standalone email warmup system. GMass shut down its dedicated warmup feature back on January 31st, 2023, after Google flagged the practice as an API policy violation. So if you're searching for "gmass warm up" hoping to spin up automated inbox activity through GMass the way you could a few years ago, that tool isn't there anymore. GMass still exists as a solid Gmail-based cold email platform — but for warming up new inboxes in 2026, you'll need a different approach. This review covers what happened, what GMass offers now, and which email warmup software actually keeps you out of spam.

What Happened to GMass Warm Up?

GMass built its reputation as a Gmail mail-merge and cold email tool that lives right inside your inbox. At one point it also ran a free email warmup network — automated accounts that would send, open, and reply to each other to build up sending history.

That warmup network got shut down in early 2023. GMass announced it publicly, and the reason wasn't a business decision made in a vacuum. Google objected to how warmup traffic interacted with the Gmail API — essentially, automated activity designed to trick spam filters and inflate sending volume ran against Google's API usage policies.

Google flagged warmup automation as a violation for dodging spam filters, pushing Gmail sending limits, and generating artificial engagement through the API.

To be clear: GMass the cold email platform is very much alive. Only the warmup component was discontinued. If you land on GMass's warmup page today, you'll find messaging that no longer resembles the fully automated network it once ran.

Why This Matters for Cold Emailers

A lot of outreach setups from 2021-2022 relied on GMass warmup as a free, built-in solution. If you're following an older guide or an outdated YouTube tutorial, you might waste hours trying to enable a feature that doesn't function anymore.

More importantly, the shutdown revealed something every cold emailer should internalize: warmup that abuses provider APIs is fragile. When your deliverability strategy depends on a loophole, it can vanish overnight.

Is Email Warmup Illegal or Against Google's Rules?

This is the question that comes up constantly, and the nuance matters. Warming up an email account — gradually increasing sending volume and building positive engagement — is not illegal. It's a legitimate deliverability practice.

What Google objected to was a specific implementation: using the Gmail API to run bot networks that game spam filters at scale. There's a difference between:

• Organic warmup — you send real emails, get real replies, and slowly ramp volume over weeks.
• Network-based automation — thousands of accounts artificially emailing each other to simulate reputation.

Most modern warmup tools use IMAP/SMTP connections rather than the Gmail API, which sidesteps the specific policy GMass ran into. But the underlying tension remains: warmup networks are always somewhat adversarial to mailbox providers. Understanding this helps you pick tools that are sustainable. For the full picture on how warmup works and why it matters, read What Is Email Warm Up and Why It Matters for Cold Outreach.

What GMass Offers Now (Without the Warmup)

GMass is still a capable tool for sending cold email and mail merges directly from Gmail. Here's what it does well in 2026:

• Mail merge from Google Sheets — personalize campaigns using spreadsheet data.
• Automated follow-ups — sequence replies based on whether recipients open or respond.
• Send scheduling and throttling — spread sends across time to look more natural.
• Analytics — opens, clicks, and reply tracking inside Gmail.

What it does not do anymore is warm up your inbox for you. That gap is exactly why the search volume for "gmass warm up" alternatives has climbed. If you're choosing a full sending platform, compare options in our guide to the best cold email software.

GMass Warm Up Alternatives Worth Considering

Since GMass warmup is gone, you have two paths: use standalone email warmup software, or move to managed infrastructure that includes warmup by default. Here's how the popular options stack up.

Tool	Type	Warmup Included	Best For
MailReach	Standalone warmup	Yes	Warming existing inboxes
Lemwarm (lemlist)	Warmup + sending	Yes	Teams already on lemlist
Warmup Inbox	Standalone warmup	Yes	Budget-conscious solo senders
Warmy.io	Standalone warmup	Yes	Multi-provider setups
Infinity Inboxes	Managed infrastructure	Yes (automated, built in)	Scaling cold outreach without babysitting warmup

For a deeper breakdown of features and pricing across these, see our tested rankings in Best Email Warm-Up Tools in 2026: Compared & Ranked and the free-tier roundup at Best Free Email Warm Up Tools in 2026.

Standalone Warmup Tools vs. Managed Inboxes

Standalone warmup software connects to inboxes you already own and runs engagement traffic through them. That works, but it puts the burden on you to buy domains, configure DNS, spread accounts across providers, and monitor reputation manually.

Managed infrastructure flips the model. You get inboxes that come pre-configured with authentication and warmup already running — no separate warmup subscription, no DNS wrestling. That's the model Infinity Inboxes uses.

Why Warmup Alone Isn't Enough

Here's the trap: people assume that if they just run enough warmup, their cold email will land. Warmup is necessary but nowhere near sufficient. Deliverability is a stack, and warmup is one layer.

To actually reach inboxes, you need all of these working together:

1. Proper authentication — SPF, DKIM, and DMARC records configured correctly. If these are broken, warmup won't save you. See our SPF, DKIM, and DMARC setup guide.
2. A clean sending domain — ideally a separate domain from your primary brand, so cold outreach doesn't risk your main domain reputation.
3. Warmup that ramps gradually — you don't go from zero to 200 emails a day on a fresh inbox.
4. Sender reputation management — monitoring bounce rates, spam complaints, and engagement. Learn how this works in Email Sender Reputation.
5. Good list hygiene and copy — bad targeting and spammy copy will get you flagged no matter how warm your inbox is.

Miss any one of these and you'll end up in spam even with perfect warmup. That's why we recommend treating the whole thing as infrastructure, not a single tool. Our cold email infrastructure setup guide walks through the entire stack.

How to Warm Up an Email the Right Way in 2026

Whether you use a standalone tool or managed inboxes, the mechanics of good warmup follow the same principles. Here's a practical ramp schedule for a new Google Workspace inbox.

Week	Warmup Emails/Day	Real Cold Emails/Day	Notes
1	10-15	0	Warmup only. No live sends.
2	20-25	0-5	Start light live sends to engaged lists.
3	30-40	10-20	Monitor reply and bounce rates closely.
4	40+	20-30	Keep warmup running in the background.
5+	Ongoing	30-50 max per inbox	Never fully stop warmup.

Two rules people constantly break:

• Don't stop warmup once you go live. Ongoing warmup traffic keeps your engagement signals healthy even when cold campaigns generate low reply rates.
• Don't push a single inbox past 30-50 real cold emails per day. Volume beyond that on one inbox is a reputation risk. Scale by adding more inboxes, not by hammering one.

That second point is why serious senders run multiple inboxes across multiple domains. For more on how to warm up email marketing campaigns without torching deliverability, our cold email deliverability guide goes deeper on volume distribution.

Signs Your Warmup Is Working

You want to see these indicators before you scale up live sending:

• Test emails landing in the Primary inbox, not Promotions or Spam
• Bounce rate under 2%
• Spam complaint rate under 0.1%
• Consistent engagement (opens and replies) on warmup traffic

Run inbox placement tests weekly during warmup. Tools like Google Postmaster Tools also give you domain-level reputation data straight from Google.

Should You Rebuild Your Setup Around GMass?

If you're a solo founder sending small-volume, highly personalized outreach from a single Gmail account, GMass plus a standalone warmup tool can work fine. It's affordable and lives inside the interface you already use.

But if you're a sales team, an agency, or a founder planning to scale outbound past a couple hundred emails a day, the GMass-plus-warmup-tool combo starts to creak. You'll be juggling:

• Multiple domains and their DNS records
• Dozens of inboxes to warm and monitor
• A separate warmup subscription per inbox
• Reputation issues you have to diagnose yourself

For scaling scenarios, managed infrastructure removes most of that operational load. If you're weighing in-house versus outsourced, our piece on choosing a cold email agency or building in-house is a useful companion read.

The Infrastructure Approach to Warmup

The lesson from the GMass warmup shutdown is that deliverability shouldn't rest on a single fragile feature. It should rest on properly configured infrastructure.

That's the model behind Infinity Inboxes. Instead of buying inboxes and bolting on separate warmup software, you get managed Google Workspace inboxes starting at $3.50/month — or Outlook and Microsoft 365 inboxes — with automated warmup built in from day one. Authentication is handled, warmup runs continuously, and the inboxes are purpose-built for cold outreach deliverability.

That means no separate warmup subscription, no DNS troubleshooting, and no scrambling when a tool changes its policy. You focus on writing good campaigns and booking meetings; the infrastructure handles landing you in the inbox. If you're running outbound for SaaS specifically, pair this with tactics from our cold email for SaaS playbook and the templates in our B2B cold email guide.

Frequently Asked Questions

Does GMass still have a warmup feature in 2026?

No. GMass shut down its dedicated email warmup system on January 31st, 2023, after Google flagged the automated warmup network as an API policy violation. The GMass sending platform still works — only warmup was discontinued.

Is email warmup against Google's terms?

Organic warmup — gradually ramping volume and building real engagement — is a legitimate practice. What Google objected to was warmup networks that used the Gmail API to artificially game spam filters at scale. Most modern warmup tools use IMAP/SMTP to avoid that specific issue.

What's the best GMass warm up alternative?

For warming inboxes you already own, standalone tools like MailReach, Lemwarm, Warmup Inbox, and Warmy.io all work. If you'd rather skip the setup and monitoring, managed infrastructure like Infinity Inboxes includes automated warmup so you don't manage it separately.

How long should I warm up a new inbox?

Plan for at least 2-4 weeks of ramp before running high-volume campaigns, and keep warmup traffic running indefinitely in the background even after you go live.

Can I use GMass with managed inboxes?

Yes. You can connect Google Workspace or Outlook inboxes to a variety of sending tools. Managed inboxes handle the warmup and reputation side; your sending tool handles campaign delivery.

The Bottom Line

The "gmass warm up" feature people are searching for hasn't existed since early 2023. GMass remains a decent Gmail-based sending tool, but you'll need separate warmup software or managed inboxes to protect your deliverability now.

The smarter play in 2026 is to stop treating warmup as a bolt-on and start treating deliverability as infrastructure — proper authentication, dedicated domains, gradual ramping, and continuous warmup working together. When you're ready to skip the manual setup entirely, explore Infinity Inboxes for managed inboxes with automated warmup baked in, and check our complete deliverability guide to make sure every other layer is dialed in too.