The POST {{apiPath}}/environments/{{envID}}/emailDomains operation adds a new resource entity to the specified environment resource.

Note: An environment can have only one configured trusted email domain.

The request body must specify a value for the resource entity’s domainName property, and there cannot be an existing trusted email domain resource associated with the specified environment. If a trusted email domain resource already exists for this environment, the response returns a UNIQUENESS_VIOLATION error.