(a) Complaint. The complaint or a copy thereof may be served upon the respondent by certified mail, or first-class mail as hereinafter provided, by delivering it to the respondent or his/her attorney or agent of record either in person or by leaving it at the office or place of business of the respondent, attorney or agent, or in any other manner that has been agreed to by the respondent. Where the service is by certified mail, the return post office receipt duly signed by or on behalf of the respondent shall be proof of service. If the certified mail is not claimed or accepted by the respondent and is returned undelivered, complete service may be made by mailing the complaint to the respondent by first-class mail, addressed to the respondent at the last address known to the Director of Practice. If service is made upon the respondent in person or by leaving the complaint at the office or place of business of the respondent, the verified return by the person making service, setting forth the manner of service, shall be proof of such service.

(b) Service of papers other than complaint. Any paper other than the complaint may be served as provided in paragraph (a) of this section or by mailing the paper by first-class mail to the respondent at the last address known to the Director of Practice, or by mailing the paper by first-class mail to the respondent's attorney or agent of record. Such mailing shall constitute complete service. Notices may be served upon the respondent or his/her attorney or agent of record by telegraph.

(c) Filing of papers. Whenever the filing of a paper is required or permitted in connection with a disqualification proceeding under this subpart or by rule or order of the Administrative Law Judge, the paper shall be filed with the Director of Practice, Treasury Department, Internal Revenue Service, Washington, DC 29224. All papers shall be filed in duplicate.