Microsoft 365 is priced per user and built for a company's own mail. Cold email needs many mailboxes on separate domains. Here is how Microsoft seats, Azure inbox sellers and Winnr's SMTP mailboxes compare, and when Microsoft is still the right call.
Teams that send cold email from Outlook mailboxes usually get them one of three ways: they buy Microsoft 365 or Exchange Online seats in their own tenant, they buy Azure inboxes (also sold as Entra or Outlook inboxes) from a seller who provisions Microsoft tenants for them, or they use mailboxes they already have. All three send through Microsoft's network, which is the reason people want them: when most of your prospects sit on Microsoft 365, sending from Microsoft feels like the safe match.
Winnr is the fourth option. Its mailboxes are SMTP and IMAP accounts on Winnr's own sending infrastructure, not Microsoft accounts. They cost less per mailbox than Microsoft's list prices, carry more cold email per mailbox than most Azure inbox offers, and log in with a plain username and password, so Microsoft's retirement of Basic Authentication for SMTP AUTH does not touch them. What you give up is the Microsoft network and the Outlook interface.
List prices as of October 2026, against Winnr's plans.
| Mailboxes | Exchange Online (Plan 1), $4/user | Microsoft 365 Business Basic, $7/user | Winnr |
|---|---|---|---|
| 50 | $200/month | $350/month | $69/month (Startup) |
| 200 | $800/month | $1,400/month | $189/month (Enterprise) |
| 1,000 | $4,000/month | $7,000/month, across several tenants (Business plans are sold for up to 300 users) | $989/month (Enterprise + 800 extra mailboxes at $1) |
| Per mailbox | $4.00 | $7.00 | $0.95 to $1.38 |
Microsoft prices from microsoft.com (Exchange Online and Microsoft 365 business plans), checked October 6, 2026, US list prices per user per month, paid yearly on an annual subscription. Exchange Online Plan 1 is email only (50 GB mailbox); Business Basic adds Teams, web Office apps and 1 TB of storage. Domains are left out on both sides; on Winnr they are a one-time purchase (a .com is about $13) or free to connect. Warming on Winnr is optional at $0.60 per mailbox per month.
Azure inbox sellers create Microsoft 365 mailboxes in tenants they set up for you and sell them far below Microsoft's list price per seat. The catch is volume: these offers put many mailboxes on one domain and rate each mailbox at a few emails a day, so the price per mailbox is not the price per email. Two published examples:
| Offer (as of October 2026) | Price | Stated volume | Cost per 1,000 emails |
|---|---|---|---|
| Puzzle Inbox, Outlook inboxes | $0.35 per inbox per month ($0.50 pre-warmed), 100 inboxes per domain | 3 emails per inbox per day | About $3.89 (90 emails per inbox over 30 days) |
| Hypertide Entra | $25 per domain per month, 25 inboxes included | 2,200+ emails per domain per month (business days) | About $11.36 |
| Winnr Startup | $69 for 50 mailboxes ($1.38 each) | 10 to 20 cold emails per mailbox per day (15 used here) | About $3.07 |
| Winnr Enterprise | $189 for 200 mailboxes ($0.95 each) | 15 cold emails per mailbox per day | About $2.10 |
Sources: puzzleinbox.com/pricing and hypertide.io, checked October 6, 2026. Cost per 1,000 emails is our arithmetic from each provider's own published price and volume. Winnr mailboxes can send about 50 emails a day including warming; the 15 used here is the cold portion we recommend.
The other cost of density is risk. When 25 or 100 mailboxes share one domain, a single blocklisting or reputation problem on that domain hits all of them at once. Winnr's purchase flow puts 5 mailboxes on a domain by default for the opposite reason. Our article on Azure inboxes and domain blocklists covers the mechanism. For provider-by-provider detail, see Hypertide alternative and Puzzle Inbox alternative.
Many cold email setups log in to smtp.office365.com with an email address and a password or app password. That is Basic Authentication, and Microsoft is retiring it for SMTP AUTH. After postponing the original 2026 rollout, Microsoft's current timeline is:
| When | What happens to Basic Auth for SMTP AUTH |
|---|---|
| Now to December 2026 | No change where it is enabled today |
| End of December 2026 | Disabled by default in existing tenants; admins can turn it back on |
| Tenants created after December 2026 | Not available by default; OAuth is the supported method |
| Second half of 2027 | Microsoft announces the final removal date |
Source: Microsoft's Exchange Team blog, January 27, 2026. App passwords are a form of Basic Auth and stop working at the same point. Full timeline, sources and migration steps: Microsoft 365 for cold email in 2026.
Staying on Microsoft after that means OAuth: an app registration in Microsoft Entra ID or your sequencer's Microsoft sign-in, admin consent in each tenant, and tokens that must be refreshed and that can be revoked by a password change, a Conditional Access policy or 90 days of inactivity. Agencies running mailboxes across many client tenants feel this most.
Winnr mailboxes connect over SMTP on port 465 and IMAP on port 993 with the full address and a password. There is no tenant, no admin consent and no token to expire, and the credentials go into your sequencer through a ready-made export file.
Exchange Online's published limits are generous on paper: 10,000 recipients per mailbox per day, 30 messages a minute, and a tenant-wide daily cap on external recipients that scales with your license count (trial tenants are capped at 5,000). The constraint that matters for cold email is not the number. Microsoft's own service description says customers who need to send legitimate bulk commercial email should use third-party providers that specialize in it. How that applies to any one cold email program is Microsoft's call.
On the receiving side, two changes affect anyone emailing Microsoft-hosted prospects, whatever they send from. Since May 5, 2025, Outlook.com requires SPF, DKIM and DMARC from domains sending more than 5,000 messages a day to its consumer addresses. And Microsoft Defender for Office 365 is rolling out promotional-mail tagging (Message Center MC1279093, worldwide from late July to late October 2026), which can move marketing-style mail into a Promotions folder. Plain, personal messages hold up best. Winnr publishes SPF, DKIM and DMARC at p=reject on every domain it sets up.
Microsoft mailboxes fit these cases better than SMTP.
SMTP mailboxes fit these cases better.
One honest caveat about warming: Winnr's warming network includes very few Outlook.com and Hotmail addresses, and Winnr cannot aim warming at a single provider. If most of your list is on Microsoft, run a seed placement test to Microsoft addresses before you scale. Many teams split their volume: Microsoft or Google inboxes for the prospects where provider matching matters, Winnr mailboxes for the rest. Keep your company's own Microsoft 365 on your main domain either way, and never send cold email from it.
Comparing against Google instead? Read our Google Workspace alternative for cold email, and for all three side by side, SMTP vs Google and Microsoft.
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Extra email accounts are $1/month each on either plan. Warming is $0.60/mailbox/month. Full pricing.
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