The amount of actual, direct economic damages that are recoverable is reduced to the extent such damages reasonably could have been mitigated by the plaintiff. An action for damages filed in federal district court may not be maintained unless the taxpayer has filed an administrative claim pursuant to paragraph (f) of this section and has waited the period required under paragraph (e) of this section.
For purposes of this paragraph, a duly authorized representative is any attorney, certified public accountant, enrolled actuary, or any other person permitted to represent the taxpayer before the Internal Revenue Service who is not disbarred or suspended from practice before the Internal Revenue Service and who has a written power of attorney executed by the taxpayer.
26 C.F.R. §301.7432-1