26 CFR § 301.6212-1 - Notice of deficiency.
(a) General rule. If a district director or director of a service center (or regional director of appeals), determines that there is a deficiency in respect of income, estate, or gift tax imposed by subtitle A or B, or excise tax imposed by chapter 41, 42, 43, or 44, of the Code, such official is authorized to notify the taxpayer of the deficiency by either registered or certified mail.
(b) Address for notice of deficiency -
(1) Income, gift, and chapter 41, 42, 43, and 44 taxes. Unless the district director for the district in which the return in question was filed has been notified under the provisions of section 6903 as to the existence of a fiduciary relationship, notice of a deficiency in respect of income tax, gift tax, or tax imposed by chapter 41, 42, 43, or 44 shall be sufficient if mailed to the taxpayer at his last known address, even though such taxpayer is deceased, or is under a legal disability, or, in the case of a corporation, has terminated its existence.
(2) Joint income tax returns. If a joint income tax return has been filed by husband and wife, the district director (or assistant regional commissioner, appellate) may, unless the district director for the district in which such joint return was filed has been notified by either spouse that a separate residence has been established, send either a joint or separate notice of deficiency to the taxpayers at their last known address. If, however, the proper district director has been so notified, a separate notice of deficiency that is a duplicate original of the joint notice, must be sent by registered mail prior to September 3, 1958, and by either registered or certified mail on and after September 3, 1958, to each spouse at his or her last known address. The notice of separate residences should be addressed to the district director for the district in which the joint return was filed.
(3) Estate tax. In the absence of notice, under the provisions of section 6903 as to the existence of a fiduciary relationship, to the district director for the district in which the estate tax return was filed, notice of a deficiency in respect of the estate tax imposed by chapter 11, subtitle B, of the Code shall be sufficient if addressed in the name of the decedent or other person subject to liability and mailed to his last known address.
(c) Further deficiency letters restricted. If the district director or director of a service center (or regional director of appeals) mails to the taxpayer notice of a deficiency, and the taxpayer files a petition with the Tax Court within the prescribed period, no additional deficiency may be determined with respect to income tax for the same taxable year, gift tax for the same “calendar period” (as defined in § 25.2502-1(c)(1)), estate tax with respect to the taxable estate of the same decedent, chapter 41, 43, or 44 tax of the taxpayer for the same taxable year, section 4940 tax for the same taxable year, or chapter 42 tax of the taxpayer (other than under section 4940) with respect to the same act (or failure to act) to which such petition relates. This restriction shall not apply in the case of fraud, assertion of deficiencies with respect to any qualified tax (as defined in paragraph (b) of § 301.6361-4) in respect of which no deficiency was asserted for the taxable year in the notice, assertion of deficiencies with respect to the Federal tax when deficiencies with respect to only a qualified tax (and not the Federal tax) were asserted for the taxable year in the notice, assertion of greater deficiencies before the Tax Court as provided in section 6214(a), mathematical errors as provided in section 6213(b)(1), termination assessments in section 6851 or 6852, or jeopardy assessments as provided in section 6861(c). Solely for purposes of applying the restriction of section 6212(c), a notice of deficiency with respect to second tier tax under chapter 43 shall be deemed to be a notice of deficiency for the taxable year in which the taxable event occurs. See § 53.4963-1(e)(7)(iii) or (iv) for the date on which the taxable event occurs.