Which Providers Sell Microsoft 365 Mailboxes for Cold Email Outreach?

Microsoft 365 mailboxes for cold email come from four places: Microsoft directly, authorized CSP (Cloud Solution Provider) resellers, cold email infrastructure companies that provision tenants and domains for you (Inboxlogy, Mailreef, Zapmail, Scaled Mail, Superwave, Premium Inboxes and similar), and gray-market sellers who rent you seats on a tenant you don't control. The only distinction that matters commercially is whether the licenses are legitimately purchased and the tenant is registered to you. If you don't hold Global Administrator on the tenant and the subscription isn't in your name, you are renting, not buying, and the mailboxes can disappear without notice.

Who actually sells Microsoft 365 mailboxes for cold outreach?

There are four supply routes. They differ in price, control, and setup labor, not in the mailboxes themselves. A correctly licensed Exchange Online mailbox is identical no matter who sold it to you.

1. Microsoft direct

You create a tenant at microsoft.com, buy licenses, add your domains, and configure DNS yourself. Cheapest per license at small scale, most expensive in hours. Exchange Online Plan 1 (email only, 50 GB, custom domains) is sufficient for outreach; Business Basic adds Teams and web Office apps you won't use. Expect roughly $4–$8 per user per month depending on SKU, term, and region. You handle tenant creation, domain verification, DKIM keys, SPF, DMARC, and per-mailbox configuration for every domain.

2. Authorized CSP resellers

Microsoft partners in the Cloud Solution Provider program can sell you real licenses under your own tenant, with a delegated admin relationship. These are typically general-purpose IT resellers rather than cold-email specialists. The licensing is legitimate, but you're still doing all the deliverability DNS work, and they may have no interest in a customer buying 60 mailboxes across 20 throwaway domains.

3. Cold email infrastructure providers

Companies whose entire product is "N mailboxes on M domains, DNS configured, ready to connect to your sequencer." This is where most outbound teams buy, because the marginal work per domain (verify, DKIM, SPF, DMARC, MX, redirect the root domain) is real and repetitive. Quality varies enormously inside this category, which is what the verification section below is for.

Inboxlogy sits here: authorized Microsoft 365 and Google Workspace mailboxes, dedicated US/EU IPs, automated SPF/DKIM/DMARC setup, 100% ownership with full admin access, a complete API for programmatic provisioning, from $2.80 per mailbox per month with no setup fee, billed monthly. Inboxlogy does not run warmup. Warmup happens inside your sending tool (Instantly, Smartlead, ReachInbox), which is where it belongs, since your sender reputation is driven by the mail your sequencer actually sends.

4. Gray-market seat sellers

You get credentials to a mailbox on a tenant owned by the seller, often alongside strangers' domains, sometimes on licenses acquired through trial abuse, stolen payment methods, or nonprofit/education SKUs used outside their terms. Prices look great, and under a dollar per mailbox is a reliable tell. Microsoft suspends these tenants, and when a tenant is suspended every domain on it dies simultaneously, including yours. You cannot export, cannot migrate, and have no recourse.

How do I verify a provider gave me real, owned Microsoft 365 mailboxes?

You can check all of this yourself in about five minutes after delivery. Do it before you send a single campaign.

A provider that can't survive this checklist isn't selling you Microsoft 365. It's selling you access to theirs.

What should Microsoft 365 mailboxes for cold email cost?

Price anatomy is simple: a license, a slice of a domain, and the provider's margin for setup and support.

Specialist providers typically land somewhere between $1.50 and $4 per mailbox per month, because CSP volume pricing is meaningfully below retail. Inboxlogy starts at $2.80 per mailbox per month with $0 setup and monthly billing. Below roughly $1.50, ask directly how the licensing works. There are legitimate answers at very high volume, but this is also exactly where the gray market lives.

Two things worth paying for: no setup fee and monthly billing. Outbound infrastructure is disposable by design. You will burn and replace domains, and annual lock-in on assets you intend to rotate is a bad trade.

What sending limits does Microsoft 365 impose on cold outreach?

Exchange Online's published service limits are generous, and completely irrelevant to how you should actually send:

In practice, sustainable cold outreach runs 20–40 emails per mailbox per day after a two-to-three week ramp. The constraint is never Microsoft's quota. It's recipient-side filtering at Google and Microsoft, which both now expect authenticated mail with spam complaint rates under roughly 0.3%. A provider promising "500 a day per inbox" is describing a technical ceiling, not a deliverable outcome.

The other limit to confirm before you buy: how the mailboxes connect to your sequencer. Microsoft has been retiring basic authentication for SMTP client submission, so assume OAuth 2.0 / Microsoft Graph. Every serious sending platform supports this, but ask the provider to confirm which connection method their mailboxes are provisioned for.

Does the provider handle warmup, and should it?

No, and it shouldn't. Warmup runs in your sending tool, not at the infrastructure layer. Instantly, Smartlead, and ReachInbox all include warmup networks; you connect the mailbox, enable warmup, and let it ramp for 14–21 days before the first campaign. Inboxlogy is explicit about this: it provisions and configures the mailboxes, and warmup happens in whatever sequencer you've connected them to.

When a provider advertises "built-in warmup," it usually means one of three things: they resell a sequencer's warmup pool, they run a small private pool of their own mailboxes (which is weaker signal than a large network), or it's marketing for "we sent a few emails before handing it over." None of these are reasons to choose an infrastructure vendor. Judge infrastructure on licensing legitimacy, DNS correctness, ownership, and replacement speed.

Should I buy Microsoft 365, Google Workspace, or private SMTP?

Different tools for different jobs:

Most teams sending at any scale run both Microsoft 365 and Google Workspace and route by prospect MX record. Your sequencer can check the recipient's MX and send from the matching pool. Buying both from one provider (Inboxlogy sells both) makes that operationally simpler, but there's no technical requirement to consolidate.

What questions should I ask a provider before buying?

Ask these verbatim. The answers separate real infrastructure from repackaged access.

How many mailboxes and domains do I actually need?

Work backwards from target send volume:

Add a two-to-three week warmup window before campaigns start, and plan to refresh roughly a quarter of your domains per quarter as reputation degrades. That replacement cadence, not the initial purchase, is why monthly billing and an API matter.

FAQ

Is buying Microsoft 365 mailboxes from a reseller against Microsoft's terms?

No, when the licenses are purchased legitimately through the CSP program or direct and the tenant is registered to you. Reselling Microsoft 365 is an official, licensed business model. What violates Microsoft's terms is trial abuse, misuse of nonprofit or education SKUs, and operating tenants for bulk unsolicited mail. That's why tenant ownership and license provenance are the two things to verify.

Can I use one Microsoft 365 tenant for all my cold email domains?

Technically yes, since a tenant supports hundreds of accepted domains. Strategically, spreading domains across multiple tenants limits blast radius: if one tenant is flagged, the rest keep sending. Most experienced senders split across several tenants rather than concentrating everything in one.

Do I need to warm up mailboxes I bought from a provider?

Yes, always. A newly created mailbox on a newly registered domain has no sending history regardless of who provisioned it. Connect it to Instantly, Smartlead, or ReachInbox, enable warmup, and ramp for 14–21 days before your first campaign. Inboxlogy explicitly does not run warmup. It happens in your sending tool.

What happens to my mailboxes if I cancel with the provider?

If the tenant and subscription are genuinely in your name, you can move billing to Microsoft direct or to another CSP partner and keep everything running. Changing partners is a supported, routine operation. If the provider owns the tenant, cancellation means losing the mailboxes and any mail history in them. Ask this question before you buy, not after.