Where the supervisory authority of another member or contracting state wishes, in proceedings under that state's provisions on insurance supervision, to transmit a document to an insurance undertaking active there with its registered office domestically, direct transmission by post is permissible under the provisions applicable to postal traffic with that other member or contracting state. Sending the document as a registered letter with the special forms of dispatch "personal delivery" and "return receipt" suffices as proof of service. Where service cannot be effected directly by post, or this is not expedient given the nature or content of the document, service is effected by the Federal Institute.