21. Rule 20 shall not apply to or render invalid or insufficient any mode of service in any foreign country with which a Convention has been or shall be made which is otherwise valid or sufficient according to the procedure of the Court and which is not expressly excluded by the Convention made with that foreign country. Air mail 22. The Court or Judge, in giving leave to serve a document out of the jurisdiction under these Rules, may in an appropriate case direct that the air mail service shall be used by the party effecting service. Service for foreign tribunals 23. (a) (b) (c) Where, in any civil cause or matter pending before a court or tribunal in any foreign country with which a Convention in that behalf has been or shall be made, a request for service of any document on a person within the jurisdiction is received by the Chief Judge from the consular or other authority of the country, the following procedure shall, subject to any special provision contained in the Convention, be adoptedThe service shall be effected by the delivery of the original or a copy of the document, as indicated in the request and the copy of the translation, to the party or person to be served in person by an officer of the court, unless the Court or a judge in Chambers thinks fit otherwise to direct; no court fees shall be charged in respect of the service but the particulars of charges of the officer employed to effect service shall be submitted to the Chief Registrar of the Court who shall certify the amount properly payable in respect thereof; The Chief judge shall transmit to the consular or other authority making the request, a certificate establishing the fact and the date of the service in person, or indicating the reason for which it has not been possible to effect it, and at the same time shall notify to the said consular or other authority the amount of the charges certified under paragraph (b) of t h i s rule. Substituted Service 24. Upon the application of the Attorney-General of the Federation, the Court or a Judge in Chambers may make all such orders for substituted service or otherwise as may be necessary to give effect to rules 13 to 22 of this order. Order thereon 25. Any order giving leave to effect service out of the jurisdiction shall prescribe the mode of service, and shall limit a time after the service within which the defendant is to enter an appearance, such time to depend on the place or country where or within which the writ is to be served, and the Court may receive an affidavit or statutory declaration of such service having been effected as prima facie evidence thereof. C - GENERAL PROVISIONS Where violence threatened 26. Where the officer of Court or person charged with the service of any writ or document on any person is prevented by the violence or threats of such person, or any other person in concert