D.C. Mun. Regs. tit. 9, r. 9-311
The Deputy Chief Financial Officer shall notify each owner of taxable property by mail of the assessment of the owner's real property for the next fiscal year.
The notice or accompanying statement shall include all of the information required by D.C. Official Code § 48 -824(b)(3).
Notices shall be mailed as soon as possible after January 1st of each year, but not later than March 1st of each year (unless extended under D.C. Official Code § 47-824(b)(4) ).
Unless otherwise specified, any notice, bill, or statement required by this chapter or other applicable provision of law to be served upon the property owner shall be deemed to be served when mailed by first class mail to the last known address of the property owner as recorded in the real estate assessment records of the District.
Appeals (for which a letter of agent authorization is submitted or shall be submitted) shall be filed electronically where the agent or agent's employer submits five (5) or more appeals during any tax year. For the purposes of this section, the term "agent" and the phrase "agent's employer" means any person which represents a real property owner, whether itself or through its employees, during an assessment appeal for which the person does not have an equity interest in, either directly or indirectly, or is not directly employed by, the real property owner.
D.C. Mun. Regs. tit. 9, r. 9-311