The volume model of cold email — 20–30 emails per mailbox per day, multiplied across hundreds or thousands of mailboxes — only works because a layer of vendors will rent you a mailbox for less than a coffee. In October 2026 a Google Workspace mailbox from a cold-email reseller costs $2.50–$4.50 a month, a private-SMTP mailbox as little as $0.49, and a whole Microsoft domain with 25 mailboxes $25–$50. That price floor is what lets an agency run 3,000–8,000 inboxes.
The layer is commoditised (ten-plus vendors sell near-identical Google inboxes within a dollar of each other), fragile (it depends on Google and Microsoft tolerating it — see Provider crackdowns), and being absorbed by Instantly and Smartlead, which now sell inboxes in-app.
Infrastructure is no longer a separate market a sequencer can ignore. It is becoming a line item on the sequencer's invoice — and the sequencers that bundle it set the price everyone else must match.
What is being sold
Four products sit in this layer, and most vendors sell two or three of them:
| Product | What you get | Typical price (Oct 2026) | Per-mailbox daily cap the vendor sets |
|---|---|---|---|
| Google Workspace mailbox | A user on a Workspace tenant the reseller controls or creates for you | $2.50–$4.50/mo | 15–30 |
| Microsoft 365 mailbox | A user on an M365 tenant; often sold per domain | $2.50–$5/mo, or $25–$50 per domain of 25 boxes | 10–30 |
| Private SMTP mailbox | A mailbox on the vendor's own mail servers and IPs | $0.49–$4/mo | 10–20 |
| Domains + DNS | .com registration, SPF/DKIM/DMARC, forwarding, tracking-domain SSL | $13–$19/yr per domain | n/a |
Add-ons on top: pre-warmed (aged) inboxes, dedicated IPs, warmup, placement tests and "replacement" guarantees when a mailbox dies.
Who sells it
| Vendor | Microsoft | SMTP / other | Scale claim (vendor) | |
|---|---|---|---|---|
| Zapmail | $3.00–3.50 extra box; plans from $39/10 | Yes (resold by Smartlead at $4.50) | — | "1M+ mailboxes set up" |
| Premium Inboxes | $3.50 → $2.80 by volume | Same price | — | "570K+ inboxes", "2,000+ customers" |
| Maildoso | — | — | $2.50 → $0.49 | "400k+ mailboxes" |
| Scaledmail | $3.50 | $50/domain (25 boxes) | $3.75/domain (4 boxes) | "230,000+ inboxes" |
| Mailforge (incl. Primeforge, Infraforge) | Primeforge $4.50 | Primeforge $4.50 | Mailforge $3 shared; Infraforge $4 + $99/IP | "10k+ businesses" |
| Inboxkit | $3.00 → $2.50 | $3.00 → $2.50; Azure tenant $30 (≤100 boxes) | — | not stated |
| Hypertide | $3.30 | Entra domain $25 (25 boxes) | — | not stated |
| Cheap Inboxes | $3.50 → $2.80 | — | — | "1000+ GTM experts" |
| Mission Inbox | — | — | $50/15 boxes; $199/30; dedicated IP per box | "50M+ emails per month" |
| Inframail | — | Flat $147 for ≤400 boxes | — | "2,000+ B2B companies" |
| ColdSire | Mixed pool | — | — | "100,000+ mailboxes" |
Sources, all fetched October 2026: Zapmail, Premium Inboxes, Maildoso pricing, Scaledmail pricing, Primeforge, Mailforge, Infraforge, Inboxkit, Hypertide, Cheap Inboxes, Mission Inbox, Inframail, ColdSire. Every scale figure is the vendor's own marketing claim.
The sequencers now sell it too. Instantly charges $5/mo for a done-for-you Google account, $10 for a pre-warmed one, $4 for an "Airmail" account and $15/yr per domain. Smartlead's SmartSenders resells named third parties: Google fresh $4.50, pre-warmed $9; Outlook via Zapmail $4.50 or InfraInbox $5; SMTP via Mailreef $3.99 or AeroSend $4.20. Salesforge owns the Forge stack outright. So three of the volume sequencers are also infra vendors.
Instantly's AirMail help article (10 August 2026) describes "owned, aged IPs" at $4 per account, 20 emails per mailbox per day, and availability "limited to 5,000 accounts per week" — the largest sequencer hedging away from Google.
How provisioning works
There are four ways a vendor gets you a mailbox, and they carry very different risk:
- Reseller-provisioned Workspace or M365 tenant per customer or per domain. The vendor uses Google or Microsoft partner/reseller channels and creates tenants; Primeforge says its boxes are "provisioned directly under Google or Microsoft with full admin access". Inboxkit, Cheap Inboxes and Premium Inboxes all advertise admin access.
- Shared tenants or pooled panels. Many customers' domains on one tenant, or accounts carved out of EDU, nonprofit or legacy G Suite programmes. This is what Google suspended in autumn 2025: Primeforge describes "panels" that "posed as educational institutions or charities" (Primeforge).
- Azure / Entra tenants. Cheap Microsoft tenants holding many domains and users: Inboxkit sells a tenant for $30/mo holding up to 100 mailboxes, Hypertide $25 per domain including 25 inboxes. Maildoso warns these tenants carry a very low safe send rate (2 emails per mailbox per day in its comparison).
- Private SMTP. The vendor runs its own MTAs and IPs (Maildoso, Mailforge, Infraforge, Mission Inbox, Instantly AirMail, Mailreef). No account to suspend — but reputation is the vendor's IP pool (see Google vs Microsoft vs SMTP).
How resellers sell a Google Workspace mailbox for $2.50–3.50 when Google's Business Starter list price is about $7 (EmailBison vendor blog; Google's own pricing page did not render for this pass) is not documented by any vendor. Reseller discounts alone would not explain a 50–65% gap. Treat sub-$3 Google inboxes as a provenance question.
The economics: cost per 1,000 emails
Mailbox price means little on its own; what matters is cost per email sent at the cap the vendor tells you to respect. My arithmetic below assumes 22 sending days a month, the vendor's own daily cap, and domain cost spread across the mailboxes on it.
| Setup (Oct 2026 price) | Emails/mailbox/day | Approx. cost per 1,000 sent |
|---|---|---|
| Maildoso SMTP at $0.49 | 15 | ~$1.50 + domains |
| Inframail flat $147 at its 80,000/mo cap | n/a | ~$1.80 |
| Scaledmail SMTP, $3.75/domain of 4 | 10 | ~$4.30 + domain |
| Reseller Google at $3.50, 3 per domain | 25 | ~$7 |
| Scaledmail Microsoft, $50/domain of 25 | 10 | ~$9 |
| Instantly AirMail at $4, 5 per domain | 20 | ~$9.70 |
| Reseller Google at $3.50, cautious 15/day | 15 | ~$12 |
| Retail Google Workspace (~$7) | 25 | ~$13 |
| Instantly pre-warmed Google at $10 | 25 | ~$19 |
Maildoso frames the same thing differently: $33/month per 1,000 emails/day of capacity versus $165 on Google Workspace and $250 on Azure tenants — a vendor comparison, but the arithmetic checks out against its stated caps.
A campaign of 1,000 emails a day (≈22,000 a month) needs about 40 Google mailboxes on ~14 domains: roughly $140 in mailboxes plus ~$16/month in amortised domains — before the sequencer, data or verification. See Volume math: what 10k and 100k emails a day cost and Unit economics.
How big is this layer
No analyst sizes it. The vendors' own claims give a floor: Premium Inboxes (570K), Maildoso (400K), Scaledmail (230K) and ColdSire (100K) claim about 1.3 million mailboxes under management between them; Zapmail claims "1M+ mailboxes set up", a cumulative figure. At $2.50–3.50 a month, 1.3M mailboxes is roughly $40–55M a year for those four alone — my estimate on unaudited claims. Add Zapmail, the Forge stack, Inboxkit, Hypertide and the sequencers' own resale, and a $100M+ annual run-rate for the whole layer is plausible but unproven.
Customer scale is lopsided. Premium Inboxes says it serves "10-inbox startups to 8,000-inbox agencies"; a Cheap Inboxes testimonial mentions "almost 3k inboxes". The big buyers are Lead-gen agencies.
No revenue, funding or founder data was found for Zapmail, Scaledmail, Premium Inboxes, Inboxkit, Hypertide or Cheap Inboxes. Maildoso's site names its entity as "BacklinkSwappers, inc." in San Francisco. This layer is mostly private, bootstrapped and opaque.
Where the margin goes
- Resellers compete on price: Premium Inboxes and Cheap Inboxes bottom out at $2.80, Inboxkit at $2.50 annual. Differentiation is reduced to setup speed ("5 minutes", "<6 hours"), replacement guarantees and Slack support.
- Sequencers capture the spread. Smartlead buys Zapmail's Outlook boxes and sells them at $4.50; Instantly sells a Google box at $5 or a pre-warmed one at $10 — double the reseller market rate. Pre-warming is worth about $4.50–5 per mailbox per month in both price lists.
- Private-SMTP operators have the best gross margin (they own the servers) and the most reputation risk.
Platform policy: Google's autumn 2025 wave hit an estimated ~25% of clients at "reputable infrastructure providers" (Salesforge newsletter, vendor estimate; see Provider crackdowns and Provider rules: Google, Microsoft and the ESPs). Lock-in: Instantly's pre-warmed accounts can only be used inside Instantly, and Instantly keeps domain ownership and admin access (Instantly help).
What this means for an entrant
- Bundle infra on day one, or lose the agency buyer. Instantly and Smartlead already sell inboxes in-app; an agency will not adopt a sequencer that sends them to five other vendors. Resell two or three suppliers (Smartlead's model) before building anything. See Infrastructure strategy: build or partner.
- Do not compete on price per Google mailbox. It is $2.50–3.50 and falling, with ten sellers. Compete on what the cheap sellers do not do: customer-owned domains, export, provenance you can prove, automatic replacement.
- Portability is the counter-position to Instantly. Instantly keeps domain ownership of pre-warmed accounts. "Your domains, your tenants, take them with you" is a clean wedge.
- Plan for multi-provider failover. Build the sending engine to move a domain from Google to Microsoft to SMTP without a migration project. That is the product every buyer wanted in October 2025. See Sending architecture.
- Owning SMTP is the long game, not the MVP. Instantly needed years and scale before launching AirMail with a 5,000-accounts-per-week throttle. An entrant should rent, measure, then decide. See Build costs and team.