26 C.F.R. § 301.6091-1
Place for filing returns and other documents
(a) General rule. For provisions concerning the place for filing returns, including hand-carried returns, see the regulations relating to the particular tax. Except as provided in paragraph (b) of this section, for provisions concerning the place for filing documents other than returns, see the regulations relating to the particular tax.
(b) Exception for hand-carried documents other than returns. Notwithstanding any other provisions of this chapter—
(1) Persons other than corporations. If a document, other than a return, of a person (other than a corporation) is hand carried, and if the document is otherwise required to be filed with a service center, such document may be filed with any person assigned the responsibility to receive hand-carried returns in the local Internal Revenue Service office that serves the legal residence or principal place of business of such person, or, in the case of an estate, the local Internal Revenue Service office serving the domicile of the decedent at the time of his death. A document may also be filed by hand carrying such document to the appropriate service center, or, in the case of a document required to be filed with an office of the Alcohol and Tobacco Tax and Trade Bureau, by hand carrying as specified in regulations of the Alcohol and Tobacco Tax and Trade Bureau, see, 27 CFR chapter I, subchapter F.
(2) Corporations. If a document, other than a return, of a corporation is hand carried, and if the document is otherwise required to be filed with a service center, such document may be filed with any person assigned the responsibility to receive hand-carried returns in the local Internal Revenue Service office that serves the principal place of business or principal office or agency of the corporation. A document may also be filed by hand carrying such document to the appropriate service center, or, in the case of a document required to be filed with an office of the Alcohol and Tobacco Tax and Trade Bureau, by hand carrying as specified in regulations of the Alcohol and Tobacco Tax and Trade Bureau, see, 27 CFR chapter I, subchapter F.
(c) Definition of hand carried. For purposes of this section and section 6091(b)(4) and the regulations issued thereunder, a return or document will be considered to be hand carried if it is brought to the any person assigned the responsibility to receive hand-carried returns in the local Internal Revenue Service office by the person required to file the return or other document, or by his agent. Examples of persons who will be considered to be agents, for purposes of the preceding sentence, are: Members of the taxpayer's family, an employee of the taxpayer, the taxpayer's attorney, accountant, or tax advisor, and messengers employed by the taxpayer. A return or document will not be considered to be hand carried if it is sent to the Internal Revenue Service through the U.S. Mail.