Deploy and manage a Microsoft 365 tenant
Tenant and domain planning
Every tenant starts with an initial contoso.onmicrosoft.com domain that cannot be renamed or removed; routable addresses must live on a custom domain you verify by adding a TXT record (or an MX record if the domain already routes mail) in public DNS. Plan the full record set: MX for routing, one SPF TXT record (it must resolve in a single DNS lookup), two DKIM CNAMEs (selector1 and selector2._domainkey), a _dmarc TXT policy, plus Autodiscover and SIP/Intune CNAMEs for clients. After verification, set the custom domain as the default so new users receive routable addresses, and keep at least one cloud-only Global Administrator to survive a directory-sync outage.
Licensing, roles, and app deployment
Assign licenses directly or through group-based licensing, which requires a usage location on every user and enough seats; removing a user from the group removes the license. Delegate with least privilege using built-in roles (User Administrator, License Administrator, Exchange Administrator, Helpdesk Administrator) rather than Global Administrator. Deploy Microsoft 365 Apps with the Office Deployment Tool or cloud update policy, choosing an update channel: Current Channel for fastest features, Monthly Enterprise Channel for predictable monthly updates, Semi-Annual Enterprise Channel for maximum stability.
Day-to-day operations
The Microsoft 365 admin center hosts service health, the Message center, service requests, and org settings such as theme, release preferences, and password expiration. Check Service health before opening a ticket.
Rule of thumb: verify the domain and make it default before bulk-creating users, and remember a domain cannot be removed while any user, group, contact, or alias still references it.
Traps to expect: claiming DKIM needs a single CNAME; deleting the onmicrosoft.com domain; forgetting usage location when testing group-based licensing; confusing Targeted release (feature preview for a selected group) with an update channel.