A brand-new Google Workspace or Microsoft 365 mailbox has no sending history. To Gmail and Outlook, it's a stranger, and strangers sending cold email get filtered fast.
Email warmup is how that mailbox builds a track record before it sends a single cold email. Done properly, it takes about two weeks. Done badly, with too much volume too early, it burns the mailbox before the first campaign launches.
This guide covers warmup specifically for Google and Microsoft mailboxes: what to set up first, the schedule I follow, how the two providers differ, and when it makes more sense to skip the wait with pre-warmed mailboxes.
Warmup gives a new mailbox the positive sending history that inbox providers look for before they trust it.
A warmup tool connects your mailbox to a network of other real mailboxes. They exchange realistic emails, open them, reply to some, and move any that land in spam back to the inbox. Volume starts with a handful of messages a day and climbs gradually. To Gmail and Outlook, this looks like a mailbox that's being used normally and that people want to hear from.
What warmup can't do is fix a broken setup. If authentication fails, the list bounces, or the mailbox sends 150 cold emails a day, no amount of warmup will save it. That's why setup comes first.
Provider sending limits are ceilings for normal business use, not targets for cold email from a new mailbox.
Google Workspace allows up to 2,000 messages a day per user, and only 500 on trial accounts (Google's sending limits). Microsoft 365 allows up to 10,000 recipients per day per mailbox (Microsoft's sending limits). Those numbers tell you when the provider will block you outright. They say nothing about when your mail starts landing in spam, which happens far earlier for a mailbox with no history.
On top of that, Google and Yahoo have required authentication and spam complaints below 0.3% from bulk senders since February 2024, and Microsoft started routing non-compliant high-volume mail to Junk in May 2025. A cold mailbox that ramps too fast trips those filters even if it's nowhere near the official limits. This breakdown of Gmail sending limits explains how the different caps apply.
Warmup builds reputation on top of your setup, so the setup has to be right from day one.
With Primeforge, most of this is done for you. DNS records are configured automatically on every domain, profile pictures and GIFs are handled out of the box, and domain forwarding is set from inside the platform.
The process is simple; the discipline is in not rushing it.
Manual warmup, where you email friends and colleagues every day, doesn't produce enough consistent activity to matter. I connect every new mailbox to Warmforge on day one. Google Workspace and Microsoft 365 mailboxes connect directly, and if they came from Primeforge you can select them and export them straight into Warmforge.
For the first 14 days, the mailbox only sends warmup emails. The tool increases volume gradually, and you don't send any cold email.
If you need a deeper walkthrough, this Salesforge guide to email warmup covers how warmup engines work in general.
From week three, start with 5 to 10 cold emails a day per mailbox and keep warmup running in the background. Increase weekly while the mailbox stays healthy.
Warmup activity keeps balancing your cold sends with positive engagement. Mailboxes that stop warming after launch usually see placement slide within a few weeks.
This is the schedule I use for a new Google Workspace mailbox; for Microsoft 365, I stretch each stage by about a week.
| Week | Warmup emails per day | Cold emails per day | What to check before moving on |
|---|---|---|---|
| Week 1 | Ramps automatically from a few to about 10 | 0 | SPF, DKIM and DMARC pass; no warmup emails stuck in spam |
| Week 2 | About 10 to 20 | 0 | Heat Score™ climbing steadily |
| Week 3 | About 20 to 30 | 5 to 10 | Heat Score™ of 85 or above; placement test mostly inbox |
| Week 4 | Keep running | 10 to 20 | Bounce rate under 2%; no spike in spam complaints |
| Week 5 onward | Keep running | 20 to 30 maximum | Weekly placement test and blocklist check |
The exact warmup volumes depend on your warmup tool's settings; the numbers that matter are the cold sends. If you need more than about 30 cold emails a day, add mailboxes rather than pushing one harder. This guide on how many domains you need for cold email shows how to size the setup.
Both providers need warmup, but they react differently to new mailboxes.
Google mailboxes usually warm up faster and tolerate a slightly quicker ramp. The bigger risk is account-level: brand-new Workspace accounts that send unusual volume early can be suspended. This guide on why Google accounts get suspended covers the triggers and how to recover.
Outlook filtering is stricter on new mailboxes and reacts quickly to sudden spikes. I ramp Microsoft mailboxes about a week slower and keep daily cold volume at the lower end of the range for longer. These Microsoft 365 throttling best practices explain the limits you'll hit.
Most B2B prospects receive email on Google or Microsoft, and each provider tends to trust mail from its own ecosystem. Warming mailboxes on both lets you use ESP matching: Google mailboxes for Google recipients, Microsoft mailboxes for Microsoft recipients.
This comparison of Google Workspace vs Microsoft 365 for cold outreach goes deeper on the differences.
Days on the calendar are a rough guide; the mailbox's actual reputation is what tells you it's ready.
I watch three signals in Warmforge before adding cold volume:
Before the first campaign, I also run an inbox placement test from the real mailbox with the real email copy. This email deliverability check walks through that last step.
When a campaign can't wait two weeks, pre-warmed mailboxes let you start sending from day one.
Pre-warmed mailboxes arrive with warmup already completed, on domains with DNS configured and professional-looking names. You choose the domains, add DMARC and domain forwarding, review the mailboxes and connect them to your sending tool.
Pre-warmed doesn't mean you can skip the rest of this guide. I still keep warmup running and ramp cold volume gradually, just from a stronger starting point. These roundups of pre-warmed Google mailboxes and pre-warmed Microsoft 365 mailboxes compare the options.
Most failed warmups I've audited come down to one of these six mistakes.
Primeforge gives you mailboxes worth warming, and Warmforge does the warming.
Primeforge provides real Google Workspace and Microsoft 365 mailboxes built for cold outreach:
Pricing runs from $4.50 to $3.50 per mailbox per month billed annually, dropping at volume. The first mailbox is live in about 30 minutes. There's no free trial because mailboxes have to be purchased, but the app is free to explore first.
Warmforge handles the warmup itself:
Primeforge is one of three infrastructure options in the Forge Stack under one login. The teams I see doing best pair it with Mailforge for shared infrastructure or Infraforge for dedicated IPs, so they always have a mailbox on the same provider as each prospect.
On Salesforge, every connected mailbox is warmed by Warmforge for free, and you can run outreach with your own team, hand it to Agent Frank, Salesforge's AI SDR, or bring in a certified Forge Expert agency. Once warmup is done, this guide to improving email deliverability covers what keeps the mailbox healthy.
Warmup is the cheapest insurance in cold email, as long as the mailbox underneath it is worth warming.
Start with real Google Workspace and Microsoft 365 mailboxes on secondary domains, set up properly before the first email. Warm them for about two weeks, add cold volume slowly, keep warmup running, and let Heat Score™ tell you when to scale. If you can't wait, start with pre-warmed mailboxes and follow the same ramp from there.
Primeforge covers the mailboxes, Warmforge covers the warmup, and with Salesforge, Leadsforge, Mailforge, Infraforge and Agent Frank, the whole outbound stack sits under one roof.
Quick answers to the questions I hear most about warming up Google and Microsoft mailboxes.
Email warmup is the process of building a new mailbox's sending reputation before you use it for cold email. A warmup tool exchanges realistic emails between your mailbox and a network of real mailboxes, gradually increasing volume, so providers like Gmail and Outlook learn to trust it.
About two weeks before the first cold email for a new Google Workspace mailbox, and a little longer for Microsoft 365. After that, keep warmup running and add cold volume gradually over the next two to three weeks.
Let the warmup tool handle warmup volume, which starts with a few emails a day. Send no cold email for the first two weeks, then start at 5 to 10 cold emails a day per mailbox and stay at or below 20 to 30 once the mailbox is fully warm.
No. Keep warmup running for as long as the mailbox sends cold email. Ongoing warmup activity balances your cold sends with positive engagement and keeps reputation stable.
Yes. Microsoft tends to filter new mailboxes more strictly and reacts faster to sudden volume spikes, so I ramp Microsoft 365 mailboxes about a week slower. Google mailboxes usually warm faster, but brand-new Workspace accounts can be suspended if they send unusual volume early.
Only by using pre-warmed mailboxes, which arrive with warmup already completed. Sending cold email from a brand-new, unwarmed mailbox usually lands in spam and can damage the domain for future campaigns.
Not on Google Workspace or Microsoft 365, where the provider owns and manages the sending IPs. IP warmup only applies when you send from your own dedicated IPs.
Warmforge includes unlimited warmup free with every Salesforge plan, and offers 1 free warmup slot when you sign up for Warmforge on its own. Standalone, it costs $9 per mailbox slot per month on annual billing.
