37 CFR § 1.248 - Service of papers; manner of service; proof of service in cases other than interferences and trials.
(a) Service of papers must be on the attorney or agent of the party if there be such or on the party if there is no attorney or agent, and may be made in any of the following ways:
(1) By delivering a copy of the paper to the person served;
(2) By leaving a copy at the usual place of business of the person served with someone in his employment;
(4) Transmission by first class mail. When service is by mail the date of mailing will be regarded as the date of service;
(5) Whenever it shall be satisfactorily shown to the Director that none of the above modes of obtaining or serving the paper is practicable, service may be by notice published in the Official Gazette.
(b) Papers filed in the Patent and Trademark Office which are required to be served shall contain proof of service. Proof of service may appear on or be affixed to papers filed. Proof of service shall include the date and manner of service. In the case of personal service, proof of service shall also include the name of any person served, certified by the person who made service. Proof of service may be made by:
(1) An acknowledgement of service by or on behalf of the person served or
(2) A statement signed by the attorney or agent containing the information required by this section.