All of the infrastructure cold email runs on prohibits cold email in its terms. Google's acceptable use policy bars use "to generate, distribute, publish or facilitate unsolicited mass email, promotions, advertisements, or other solicitations ("spam")" (last modified 13 October 2025). Microsoft's online-services AUP bars use "to spam" and calls bulk email "not a supported use of the service... permitted only on a 'best-effort' basis". The ESPs are stricter still.
The industry survives on the gap between what the policies say and what the providers enforce. Google and Microsoft enforce by metrics: per-mailbox volume caps, complaint rates, bounce rates and sending-pattern detection. They do not ask who consented. The transactional ESPs enforce by list provenance: they forbid purchased and scraped lists outright and, in Twilio's case, require proof of consent on demand. That difference explains the market's architecture: hundreds of cheap mailboxes rotated by a sequencer (Inbox rotation, Google vs Microsoft vs SMTP), not one ESP account.
Cold email depends on the providers continuing to enforce metrics rather than rules. If Google or Microsoft began acting on their own AUP wording ("unsolicited mass email") with consent checks, the mailbox-farm model would break. That one variable is the sector's existential risk (Provider crackdowns, Kill criteria).
Google Workspace
| Rule | Detail (as of October 2026) | Source |
|---|---|---|
| AUP | No "unsolicited mass email, promotions, advertisements, or other solicitations" | AUP |
| Suspension | Notice, then 24 hours to cure an AUP violation; immediate for security/legal issues | Terms, modified 2 Sep 2026 |
| Resellers | Services bought through unaffiliated resellers are still governed by Google's terms | Terms |
| Daily cap | 2,000 messages per user per day; 1,500 via mail merge; 500 on trial accounts | Sending limits |
| Trial gate | Limits rise only once the domain has cumulatively paid at least $100 | Sending limits |
| Breach of cap | Error, then no new messages for up to 24 hours | Sending limits |
The 2,000-a-day cap is far above what cold emailers send per mailbox. Practitioners run a few dozen per inbox per day for deliverability, not legal, reasons (Volume math: what 10k and 100k emails a day cost, Sending limits and throttling). So the binding constraint is Gmail's receiving-side filtering and the 2024 bulk-sender rules (Google and Yahoo sender rules), not the Workspace contract.
The reseller clause matters for the infrastructure layer. Vendors such as Mailforge, Zapmail, Maildoso and Scaledmail sell pre-provisioned Workspace or Microsoft inboxes. Their customers are bound by Google's AUP like anyone else, and the reseller relationship gives no protection.
We could not verify reports of Google acting specifically against reseller-provisioned cold-email inboxes, or against particular reseller partners, in 2025–2026. If that is happening it is the most important fact on this page. See Provider crackdowns.
Microsoft 365 / Exchange Online
| Rule | Detail (as of October 2026) | Source |
|---|---|---|
| AUP | No use "to spam" | Universal license terms |
| Recipient rate | 10,000 recipients per mailbox per day | Exchange Online limits |
| Message rate | 30 messages per minute; Exchange Online "is not suited for bulk-mailing scenarios" | Exchange Online limits |
| Tenant cap (TERRL) | External recipients per tenant per day scale with licence count; trial tenants capped at 5,000 | Exchange Online limits |
| onmicrosoft.com cap | 100 external recipients per organisation per 24 hours from the default MOERA domain; NDR 550 5.7.236 | Exchange Online limits |
| Outbound spam | Suspected spam routed via a "high-risk delivery pool"; accounts and tenants that exceed limits are blocked ("restricted entities") | Outbound spam protection |
| Bulk guidance | Use third-party bulk providers or Azure Communication Services | Exchange Online limits |
Microsoft has more explicit structural controls than Google. The tenant-level external-recipient cap (TERRL) ties volume to paid licences, and the 100-recipient cap on onmicrosoft.com domains ends the trick of sending from default tenant domains. Both show Microsoft treating tenants as the abuse unit. Cold-email infrastructure vendors who pack many sending mailboxes into one tenant are betting against that unit.
Microsoft's earlier plan for a per-mailbox External Recipient Rate limit of 2,000 per day does not appear on the Exchange Online limits page as of October 2026. Microsoft cancelled it on January 6, 2026, while promising unspecified "adaptive" limits with no date. See Microsoft rules: Outlook.com and Microsoft 365 limits.
Transactional ESPs: why cold email can't use them
| Provider | Policy (date) | Key wording | Enforcement trigger |
|---|---|---|---|
| Twilio SendGrid | Email Policy, updated 9 Apr 2026 | Bans "purchased or rented email lists" and addresses "obtained from the Internet or social media" without prior affirmative consent; bans snowshoeing and waterfalling; you must "promptly provide proof" of consent | Consent proof on request; AUP termination (source) |
| Mailgun (Sinch) | AUP, updated 16 Jan 2023 | Lists "bought, rented or scraped from third-parties... absolutely prohibited"; consent must be "clear, explicit and provable" | Limit, suspend, terminate; no service credits (source) |
| Amazon SES | AWS AUP + SES docs | No "unsolicited mass email"; "Do not buy, rent, or share email addresses" | Review at 5% bounce / 0.1% complaints; pause at 10% / 0.5% (source, AUP) |
| Postmark | Terms of service | "Use of a list that has been purchased or rented from a third party is prohibited"; permission-based lists only | Complaints < 0.1%, bounces < 10% (source) |
Two features rule out cold email on these services regardless of policy wording. First, shared IP pools: one cold sender's complaints damage every other customer's delivery, so the ESPs police list quality aggressively. Second, the metric thresholds: cold lists bounce and draw complaints at rates that trip SES's 5% bounce review or the 0.1% complaint lines quickly, even with verification (Email verification, Reply benchmarks). Twilio's April 2026 policy goes furthest. Scraped addresses are named explicitly, and consent must be provable on request. That is a contractual version of the CASL and Australian evidence test (Canada: CASL, Australia, New Zealand and APAC).
Some cold-email platforms send through their own SMTP or private IP infrastructure instead of Google or Microsoft mailboxes (Sending architecture, ESP matching). That avoids the ESP bans but makes the platform the abuse desk, with the duties described on Platform liability: what the sequencer itself risks.
What they say vs. what they enforce
| Provider | Says | Enforces |
|---|---|---|
| No unsolicited mass email | Volume caps, complaint rate (bulk-sender rules), behavioural filtering; consent not checked | |
| Microsoft | No spam; bulk is unsupported | Recipient caps per mailbox and tenant, MOERA cap, outbound spam filtering, tenant blocks |
| SendGrid / Mailgun / SES / Postmark | No purchased, rented or scraped lists; consent required | Bounce and complaint thresholds; consent proof on request (Twilio); manual review |
What this means for an entrant
- Build for the metric that gets mailboxes killed, and self-police before the provider does. Track per-mailbox and per-tenant complaint proxies, bounce rates and volume against Google and Microsoft thresholds. Pause automatically before the provider does it for you. A platform whose customers rarely lose mailboxes has a retention story incumbents struggle to match. See Bounce protection and Inbox placement testing.
- Design tenant-aware infrastructure for Microsoft. TERRL and the onmicrosoft.com cap mean volume per tenant, not just per mailbox, is what Microsoft constrains. Spread sending across properly licensed tenants with custom domains, and show customers their tenant headroom. See Infrastructure strategy: build or partner.
- Compliance as a feature can open better infrastructure. If a platform records per-lead provenance and a legal basis (see Cold email law: the jurisdiction matrix), it can produce the "proof of consent" or legitimate-interest record that Twilio-style policies ask for. That will not make cold email acceptable to SendGrid, but it puts the platform on the right side of the line if providers ever move from metric enforcement to rule enforcement.
- Price in provider risk. Every cold-email business depends on Google and Microsoft tolerating behaviour their AUPs prohibit. Use multiple providers, keep a path to platform-operated SMTP, and set kill criteria (Kill criteria) tied to provider policy changes.
- Don't resell Workspace or Microsoft seats as "cold email inboxes". The reseller clause gives no protection, and marketing a provider's product explicitly for an AUP-prohibited use is the easiest pattern for that provider to act against.