$ man microsoft-365

Microsoft 365

Microsoft's business email platform. Mailboxes send through Outlook/Exchange infrastructure. Your emails come from "you@yourdomain.com" but route through Microsoft's servers.

Enterprise companies disproportionately use Microsoft 365. If your ICP is enterprise, a significant chunk of your contacts have Outlook/Exchange inboxes. Sending from Microsoft 365 to Microsoft 365 improves deliverability for the same reason Google-to-Google works — providers trust their own infrastructure. But Microsoft is also stricter about cold email and harder to warm.

I use Microsoft 365 mailboxes for contacts whose MX records show Microsoft/Outlook. These mailboxes have lower daily sending limits (start at 10-15/day, ramp carefully). I split my sending infrastructure — some domains on Google Workspace, some on Microsoft 365 — so I can route to the best-matching provider. Microsoft warmup takes longer and requires more patience. I don't rush it.