2 U.S. Code § 384 - Service and filing of papers other than notice of contest
(a) Modes of service
Except for the notice of contest, every paper required to be served shall be served upon the attorney representing the party, or, if he is not represented by an attorney, upon the party himself. Service upon the attorney or upon a party shall be made:
(2) by leaving it at his principal office with some person then in charge thereof; or if the office is closed or the person to be served has no office, leaving it at his dwelling house or usual place of abode with a person of discretion not less than sixteen years of age then residing therein; or
(b) Filing of papers with clerk
All papers subsequent to the notice of contest required to be served upon the opposing party shall be filed with the Clerk either before service or within a reasonable time thereafter.
(c) Proof of service
Papers filed subsequent to the notice of contest shall be accompanied by proof of service showing the time and manner of service, made by affidavit of the person making service or by certificate of an attorney representing the party in whose behalf service is made. Failure to make proof of service does not affect the validity of such service.