Adds email domains to the form's options.blocked_email_domains, so the form refuses submissions from addresses at them. Each domain is trimmed and lowercased, and a leading @ or *@ is dropped, as PUT /forms/{id} does: @Competitor.com is stored as competitor.com. example.com blocks addresses at example.com only; *.example.com blocks every subdomain of example.com but not example.com itself, so add both to block both. Domains already on the list are left as they are, so the request is safe to repeat. A form blocks at most 100 domains. Use DELETE /forms/{id}/blockedEmailDomains to unblock one, and PUT /forms/{id}/blockPersonalEmailProviders to block personal providers such as gmail.com without listing them. Preference Center forms take no typed email address, so a list on one has no effect. The form builder saves the whole list with the form, so a save from a builder opened before this call puts back the list it loaded. Requires the permission to edit forms.