The correct options are Register the organization's custom domain with the tenant, Confirm ownership of the custom domain, and Configure DNS records for the domain.

Register the organization's custom domain with the tenant means you add example.com to the Microsoft 365 tenant so the service can issue user identities and mailboxes under that name. This registration makes the domain available in the Microsoft 365 admin center and is the initial step before verification and DNS changes.

Confirm ownership of the custom domain is required because Microsoft needs proof that you control the domain. Verification is commonly done by adding a TXT or MX record at the domain registrar and then completing the verification process in the tenant.

Configure DNS records for the domain is necessary to route email and to enable cloud services. You add MX records for mail delivery and TXT records for SPF, and you often add CNAME and SRV records for autodiscover and other service features. You may also configure DKIM and DMARC to improve email security and deliverability.

Attempt to delete the tenant's default .onmicrosoft.com domain is incorrect because the default onmicrosoft.com domain is created with the tenant and cannot simply be removed during normal setup. You do not delete the default domain as part of adding and maintaining a custom domain and it can only be removed under restricted conditions when it is not in use.

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