(a) For purposes of this subpart, service upon an applicant or registrant will be sufficient if mailed by registered mail or certified mail return receipt requested properly addressed to the applicant or registrant at the address shown on his application or any amendment thereto, and will be complete upon mailing. Where a party effects service by mail, the time within which the person served may respond thereto shall be increased by three days.(b) A copy of any notice served in accordance with paragraph (a) of this section shall also be served upon:(1) Any registrant sponsoring the applicant or registrant pursuant to the provisions of § 3.12 of this part if the applicant or registrant is an individual registered as or applying for registration as an associated person; or(2) Any futures commission merchant or retail foreign exchange dealer which has entered into a guarantee agreement in accordance with § 1.10(j) of this chapter, if the applicant or registrant is registered as or applying for registration as an introducing broker.(c) Documents served upon the Market Participants Division or upon the Division of Enforcement or filed with the Commission under this subpart shall be considered served or filed only upon actual receipt at the Commission's Washington, DC headquarters.(d) Except for the documents which may be served under § 3.51 , any documents served upon an applicant or registrant or upon the Market Participants Division or the Division of Enforcement or filed with the Commission under this subpart shall be concurrently filed with the Proceedings Clerk, together with proof of service, in accordance with the provisions of § 10.12 (d) and (e) of this chapter.49 FR 8220, Mar. 5, 1984, as amended at 57 FR 23151, June 2, 1992; 60 FR 49334, Sept. 25, 1995; 60 FR 54801, Oct. 26, 1995; 67 FR 62351 , Oct. 7, 2002; 75 FR 55427 , Sept. 10, 2010; 78 FR 22419 , Apr. 16, 2013