Provision a sending domain for a workspace. Find-or-create: returns 200 with the existing record if a domain with this name already exists for the workspace, or 201 with freshly generated DNS records if it was just created. These are email sending domains (DKIM/SPF/DMARC) - for website/hosting domains, see listDomains. The response includes the email-transport records; dkim_record can be null until the DKIM key finishes generating, and POSTing the same name again retries provisioning. Provisioning also creates a no-reply@<name> sender address on the new domain. When accessing the API through an OAuth connection from a third-party platform, this endpoint is restricted to trusted developer platforms; with your own API key (or an OAuth app acting on its own team's workspaces) it always passes. Follow next_steps, which distinguishes the required ownership step, the required transport records, and the recommended return-path record; verified SMTP replaces DKIM/SPF/DMARC. Ownership (ownership_verified) is proved by connecting the domain, as www.example.com or another subdomain of it, to this workspace as a website/hosting domain in the ClickFunnels app, not through this API. Ownership is confirmed at the root domain, so provision example.com rather than a subdomain such as mail.example.com, which is rejected with 422 naming the root domain to use instead. Then call verifyEmailsDomains until ready_for_sending is true; a 200 there means the check ran, not that it passed. The top-level verified field means transport only; sender readiness requires both ownership and transport. Return-path verification is independent. Once ready, create addresses via POST /workspaces/{workspace_id}/emails/addresses with emails_domain_id set to this domain's numeric id.