Almost every cold email cost calculation gets this wrong in the same way: it counts the mailbox price and stops. The real number includes domains, the mailbox multiplier your send volume forces on you, and the point where the whole model stops working.
Here is the actual math.
Step 1: how many mailboxes your volume forces
You do not choose a mailbox count. Your target volume chooses it for you, because per-mailbox sending limits are not negotiable.
The safe working limit is 30 to 50 sends per mailbox per day. Google’s technical limit is far higher, but technical limits are not deliverability limits, pushing a cold mailbox past 50 a day is how accounts get flagged.
| Target sends / day | Mailboxes at 40/day | With 30% headroom | Domains needed (3 each) |
|---|---|---|---|
| 200 | 5 | 7 | 3 |
| 500 | 13 | 17 | 6 |
| 1,000 | 25 | 33 | 11 |
| 2,500 | 63 | 82 | 28 |
| 5,000 | 125 | 163 | 55 |
The headroom is not optional. Mailboxes rotate out for warmup, some get flagged, and running every mailbox at its ceiling every day is itself a pattern that gets noticed.
Step 2: the real monthly cost
Take 1,000 sends a day, a normal mid-size outbound programme. That is 33 mailboxes and 11 domains.
| Line item | Direct from Google | Typical reseller ($4.50) | Outboundry ($4.00) |
|---|---|---|---|
| 33 mailboxes / month | Full retail seat pricing | $148.50 | $132.00 |
| 11 domains / year | Bought separately | Bought separately | In-app, up to $14 per TLD |
| DNS configuration | Manual, ~11 setups | Usually automated | Automated + bulk updates |
| Warmup | Separate tool | Separate tool | Unlimited, included |
| Annual mailbox spend | Highest | $1,782 | $1,584 |
Two things this makes visible. Buying direct from Google is the expensive option, not the safe one, you are paying for Docs, Drive, Meet and a productivity suite to get an SMTP endpoint. And the $0.50 gap between resellers is $198 a year at this size, which is real but smaller than most people assume.
The bigger variable is billing terms. Primeforge, for instance, charges $4.50 monthly and only reaches $4.00 on an annual commitment. Outboundry is $4.00 on monthly billing, which for an agency whose mailbox count moves with its client roster is worth more than the rate.
Competitor pricing taken from public pricing pages at the time of writing. Prices change, verify current rates before you decide.
Step 3: the costs nobody quotes
Domains. At three mailboxes per domain, 33 mailboxes means 11 domains. At $12–14 each that is roughly $150 a year, plus the work of registering them and pointing DNS if that is not handled for you.
Setup time. Provisioning 33 accounts across 11 domains by hand, configuring SPF, DKIM, DMARC and MX on each, is the better part of a day. Repeated every time you expand.
Warmup. Three to four weeks before those mailboxes can carry real volume. Budget the calendar time, not just the tool.
Replacement churn. Some mailboxes will get flagged. Assume a small ongoing replacement rate and buy headroom accordingly.
Step 4: where the model breaks
Per-seat pricing is linear. Every mailbox costs the same as the last one, forever. Infrastructure pricing is not, because the marginal cost of another mailbox on an IP and domain you already control is close to zero.
| Mailboxes | Workspace at $4 | Mailboundry from $2 | Annual difference |
|---|---|---|---|
| 20 | $80 / mo | $40 / mo | $480 |
| 50 | $200 / mo | $100 / mo | $1,200 |
| 100 | $400 / mo | $200 / mo | $2,400 |
| 200 | $800 / mo | $400 / mo | $4,800 |
The trade is sender trust. A private SMTP mailbox does not carry Google’s inherent credibility, so it needs more careful warmup and better list hygiene. What it does carry is a dedicated IP, which means your reputation is isolated and your deliverability is debuggable.
What most teams should actually do
Under 500 sends a day: Google or Microsoft mailboxes only. Roughly 17 mailboxes at $4 is $68 a month, and the platform trust is worth more than the saving.
500 to 2,000 a day: split. Keep a Workspace pool for named enterprise accounts and enterprise recipients, move volume prospecting onto private infrastructure.
Over 2,000 a day: private infrastructure as the base, with a small Workspace pool for your highest-value targets. At 82+ mailboxes the per-seat math has stopped being defensible.
Next: mailbox providers compared from $4, or when a dedicated IP is worth paying for.
Frequently asked questions
How much does Google Workspace cost for cold email?
Buying seats direct from Google costs full retail for a productivity suite you will not use. Through a reseller you should expect around $4 to $4.50 per mailbox per month. Outboundry provisions them at $4 on monthly billing.
How many Google Workspace mailboxes do I need?
Divide target daily sends by a safe limit of 30 to 50 per mailbox, then add about 30% headroom for warmup and rotation. For 500 sends a day that is roughly 12 to 17 mailboxes, so buy around 20.
How many mailboxes can I put on one domain?
Around three. More than that concentrates risk: one reputation problem on the domain takes out every mailbox on it at once. Spread across more domains with fewer mailboxes each.
Is it against Google policy to use Workspace for cold email?
Cold email itself is not prohibited, but Google enforces bulk sender requirements on authentication, spam-complaint rates and one-click unsubscribe, and will suspend accounts for high complaint volumes. Compliance is what keeps the accounts alive, not obscurity.
When should I stop using Google Workspace mailboxes?
When per-seat pricing stops being defensible, generally somewhere between 50 and 100 mailboxes. Past that you are paying seat prices for what is fundamentally an IP and a domain, and private infrastructure with dedicated IPs costs a fraction per send.