Best Email Warmup Tool for Gmail Mail Merge (2026)

Many "best email warmup tool for Gmail" lists are written for cold email teams running dozens of inboxes. If you're a founder, recruiter or small team sending a mail merge from your own Google Workspace address, you need something different: a tool that warms up one inbox, works alongside YAMM, Gmail's mail merge, GMass or a Google Sheets script, and tells you when it's safe to send.

This guide compares seven tools on what matters for that kind of sending: which email accounts they support, what they check for you, what one inbox costs, and who each one suits best.

A quick note before we start: we make Warmuply, so it's first on the list. We've been fair to the others, used only facts from their own websites, and said clearly where a rival is the better choice.

What makes the best email warmup tool for Gmail mail merge?

The best tool for a mail merge sender is one that fits how you already send, checks your domain settings, and tells you how many emails you can safely send today. Email warmup means building a sending history for your inbox by exchanging normal-looking emails with other inboxes, so Gmail and Outlook learn to trust your address before you send in bulk.

If you want the background first, here's what email warmup is and when you need it.

For mail merge senders, five things matter most:

Gmail itself asks senders to build up slowly. Its sender guidelines advise starting with a low volume to people who want your email, raising it gradually, and avoiding sudden spikes if you don't have a history of bulk sending.

The best email warmup tools at a glance

Here's how the seven tools compare on the details that matter for one Google Workspace inbox. Prices are the lowest listed monthly price for one inbox, checked on each tool's own pricing page in October 2026.

1. Warmuply: best for Google Workspace mail merge senders

Warmuply is built for people who send mail merges from their own Google Workspace address and aren't email marketers. You connect your inbox by signing in with Google, and nothing changes in how you send.

What it does:

• Warms up your inbox in the background by sending and receiving everyday-looking emails with a network of inboxes, a little more each day.
• Shows a daily safe-send number: how many emails your inbox can safely send today. You use that number in YAMM, Gmail's mail merge, GMass, Google Sheets and Apps Script, or when sending by hand.
• Checks SPF, DKIM and DMARC and explains any problem in plain English, with the exact text to paste into your domain settings.
• Runs placement tests at Gmail, Outlook and Yahoo, showing inbox, Promotions or spam.
• Sends a blacklist alert the same day if your domain lands on a spam blacklist (a public list of senders flagged for spam), with steps to get off it.

Pricing: plans are set by how many people you want to mail merge in one day: $9 a month for up to 100, $29 for up to 500, and $49 for up to 1,000. Every plan has a 7-day free trial with no credit card.

Where it's not the right fit: Warmuply supports Google Workspace addresses on your own domain only. Microsoft 365 isn't supported yet. And if you run cold email campaigns across many inboxes, a cold email platform with warmup built in will suit you better.

2. Warmup Inbox: best for simple per-inbox warmup across providers

Warmup Inbox is a dedicated warmup service that prices per inbox and supports a wide range of providers, including Gmail and Google Workspace, Outlook and Microsoft 365, Zoho, Amazon SES and SendGrid.

What it does: every plan includes spam and category monitoring, a reputation check, dashboards and outreach sequences. Higher plans add custom warmup settings, warmup in other languages and, on the top plan, a technical setup check.

Pricing: $15 per inbox a month on Basic (75 warmup emails a day), $49 on Pro (250 a day) and $79 on Max (1,000 a day). Annual billing saves 20%, and the 7-day free trial needs no credit card.

Who it suits: senders on more than one email provider who want a straightforward warmup tool, and teams adding inboxes over time, since the per-inbox price drops as you add more.

For a side-by-side look, see our Warmuply vs Warmup Inbox comparison.

3. Warmforge: best for trying warmup on one mailbox for free

Warmforge is the warmup and deliverability tool from the Salesforge family of sales products. (Deliverability means whether your emails reach the inbox instead of spam.) It works with Google Workspace and Microsoft 365 mailboxes.

What it does: warmup with AI-written emails, a "Heat Score" for each mailbox, and Health Checks that monitor your DNS and MX records (the settings on your domain that tell the internet where to deliver your email) plus your blacklist status. Every plan includes one placement test a month.

Pricing: your first workspace gets one free warming slot for a Google or Microsoft mailbox and one free placement test, renewed monthly. Extra slots started from about $10 per slot a month on its pricing calculator, with discounts for longer billing periods. Warmforge says there's no free trial beyond that, because warming needs paid slots. If you use Salesforge, warmup slots are included.

Who it suits: anyone who wants to try warmup on a single mailbox at no cost, and teams already using Salesforge.

For more detail, see our Warmuply vs Warmforge comparison.

4. MailReach: best for senders who want lots of placement testing

MailReach combines warmup with spam testing. It works with any email provider that supports SMTP (the standard way email is sent between servers), including Google Workspace, Microsoft 365 and Zoho.

What it does: warmup of up to 100 emails a day per mailbox, a reputation dashboard, and domain and inbox health checks covering blacklists, SPF, DKIM and DMARC. Each warmup plan includes at least 20 spam test credits, and one credit equals one placement test with a report.

Pricing: its pricing calculator showed about $20 per mailbox a month on the day we checked, with the price per mailbox falling as you add more. Spam test credits can also be bought on their own.

Who it suits: B2B senders, agencies and anyone who wants to run frequent placement tests. MailReach suggests an initial warmup of at least 14 days before sending campaigns.

5. Warmy: best for larger senders who want expert help

Warmy is a full deliverability platform. It works with Google Workspace and Microsoft 365, plus email platforms such as Mailchimp, HubSpot, Klaviyo and SendGrid.

What it does: every plan includes warmup through a large network of inboxes, list verification, DMARC monitoring, a deliverability tester, a reputation tracker with blacklist alerts, a template checker, and data from Google Postmaster Tools (Google's free dashboard showing how Gmail sees your domain). Plans also include a named deliverability expert.

Pricing: plans start from $49 a month, priced by how many warmup emails you need. There's a 7-day free trial with no credit card.

Who it suits: businesses sending marketing email through an email platform, or anyone who wants a person to review their setup. For a single mail merge inbox, it's likely more than you need.

6. Instantly: best for cold email teams with many inboxes

Instantly is a cold email platform, not a standalone warmup tool. Warmup comes built into its outreach plans.

What it does: the Growth outreach plan includes unlimited email accounts, unlimited warmup, 1,000 uploaded contacts and 5,000 emails a month. Higher plans add more contacts and sending volume.

Pricing: the Growth plan is $47 a month, or $37.60 a month billed yearly. You can start without a credit card.

Who it suits: teams running cold outreach from several inboxes who want sending, warmup and replies in one place. If you'd rather keep sending through YAMM, GMass or Gmail, you'd be paying for a sending platform you don't use.

7. lemlist (lemwarm): best for teams already using lemlist

lemwarm is lemlist's warmup feature. It's now part of lemlist's deliverability tools, alongside automatic domain setup, sending limits per inbox and health alerts.

What it does: lemwarm exchanges emails with other inboxes to build your sender reputation, and lemlist pauses sending before an inbox goes over a safe daily limit. A tech audit shows setup problems per mailbox.

Pricing: warmup comes with lemlist's plans rather than as a separate low-cost product. lemlist offers a 14-day free trial with no credit card.

Who it suits: sales teams already running multichannel outreach in lemlist.

Is there a cheap email warmup tool, or a free one?

Warmuply is the cheapest paid option on this list: $9 a month to warm up one Google Workspace inbox for mail merges of up to 100 people a day, with a 7-day free trial and no credit card. Warmup Inbox starts at $15 per inbox, and MailReach at about $20.

The $9 plan also shows you how many emails your inbox can safely send each day, so on the day of your mail merge you know exactly how many people to send to. It only works with Google Workspace, though. If you send from Microsoft 365, pick one of the multi-provider tools above.

What can no warmup tool fix?

No warmup tool can make people want an email they didn't expect. Warmup builds trust in your inbox and domain, but Gmail also judges every send by how recipients react to it.

What a warmup tool helps with:

• Building a sending history for a new or quiet inbox.
• Sending at a volume Gmail and Outlook will accept today.
• Getting SPF, DKIM and DMARC set up correctly.
• Spotting problems early through placement tests and blacklist alerts.

What only you control:

• Who you email. Gmail's sender guidelines say not to buy email addresses and not to email people who didn't sign up to hear from you. Old, bought or scraped lists also bring bounces and spam traps, which are addresses set up to catch spammers.
• Spam complaints. When people click "Report spam", your reputation drops fast, even on a well-warmed inbox. Google asks senders to keep the spam rate in Postmaster Tools below 0.10% and never let it reach 0.30%.
• What your email says. Misleading subject lines, fake "Re:" or "Fwd:" subjects, lots of links and pushy wording all make people more likely to hit "Report spam".

For the content side, read what really sends a mail merge to spam.

You can track your spam rate in Google Postmaster Tools.

How to choose: three questions

The right tool depends on three things: your email provider, how many inboxes you send from, and how you send.

1. Which email provider do you send from? If it's Microsoft 365 or anything other than Google Workspace, choose Warmup Inbox, Warmforge, MailReach or Warmy. Warmuply only supports Google Workspace for now.
2. How many inboxes do you send from? If you run cold outreach from many inboxes, a cold email platform like Instantly or lemlist includes warmup and handles sending too.
3. How do you send? If you send mail merges from one Workspace address with YAMM, Gmail's mail merge, GMass or a Google Sheets script, a tool built for that, like Warmuply, keeps things simple and tells you what to send each day.

Whichever you pick, give it 4 to 12 weeks before your biggest send, and test where your emails land before you send to your full list.

Before you hit send

• Check your domain settings. Run our free SPF, DKIM and DMARC checker to make sure your domain proves your emails are really from you.
• Stay under today's safe number. Send no more than your warmed-up inbox can handle, and spread a big list over several days if needed.
• Email people who expect to hear from you. Remove old or bought addresses, and include an easy way to opt out.
• Write it like a one-to-one email. Keep links to one or two and skip attachments.

Start a free 7-day trial of Warmuply. No credit card needed.