Section 64. A person aggrieved by the refusal of assessors to abate a tax on personal property at least one-half of which has been paid, or a tax on a parcel of real estate, may, within three months after the date of the assessors' decision on an application for abatement as provided in section sixty-three, or within three months after the time when the application for abatement is deemed to be denied as hereinafter provided, appeal therefrom by filing a complaint with the clerk of the county commissioners, or of the board authorized to hear and determine such complaints, for the county where the property taxed lies, and if on hearing the board finds that the property has been overrated and that the complainant has complied with all applicable provisions of law, it shall make a reasonable abatement and an order as to cost; provided, that if the tax due for the full fiscal year on a parcel of real estate is more than $5,000, said tax shall not be abated unless the full amount of said tax due, including all preliminary and actual installments, has been paid without the incurring of any interest charges on any part of said tax pursuant to section 23D, 57 or 57C of chapter fifty-nine of the General Laws; and provided further, that for the purposes of this section a sum not less than the average of the tax assessed, reduced by abatements, if any, for the three years next preceding the year of assessment may be deemed to be the tax due, provided that a year in which no tax was due shall not be used in computing such sum and if no tax was due in any of the three next three preceding years, the sum shall be the full amount of said tax due, but the provisions of said section 23D, 57 or 57C of said chapter fifty-nine shall apply to the amount of the tax deemed to be due and the payment of said sum without incurring any interest charges on any part thereof shall be deemed to be the payment of the tax. No appeal may be taken under this section with respect to a tax on property in Revere or Winthrop. Whenever a board of assessors, before which an application in writing for the abatement of a tax is or shall be pending, fails to act upon said application, except with the written consent of the applicant, prior to the expiration of three months from the date of filing of such application it shall then be deemed to be denied and the assessors shall have no further authority to act thereon; provided, that during the period allowed for the taking of an appeal including instances where the application for abatement has been denied, the assessors may by agreement with the applicant abate the tax in whole or in part in final settlement of said application, and shall also have the authority granted to them by section seven of chapter fifty-eight A to abate, in whole or in part, any tax as to which an appeal has been seasonably taken. If the list of personal property required to be brought in to the assessors was not brought in within the time specified in the notice required by section twenty-nine, no tax upon personal property shall be abated unless the board appealed to finds good cause for this delay or unless the assessors have so found as provided in section sixty-one, or unless such tax exceeds by fifty per cent the amount which would have been assessed on such estate, if the list had been seasonably brought in, and in such case only the excess over such fifty per cent shall be abated. A tax or assessment upon real estate may be abated although no list of property was brought in within the time specified by the notice required by section twenty-nine; provided, that the application for an abatement of such tax or assessment included a sufficient description of the particular real estate as to which an abatement is requested.

Upon the filing of a complaint under this section the clerk of the county commissioners or the board authorized to hear and determine the same shall forthwith transmit a certified copy of such complaint to the assessors and the assessors or the city solicitor or town counsel may within thirty days after receipt of said copy give written notice to said clerk and to the complainant that the town elects to have the same heard and determined by the appellate tax board. If the assessed valuation of the property on which the tax complained of was assessed does not exceed twenty thousand dollars and such property is occupied in whole or in part by the complainant as his dwelling, contains not more than three units designed for dwelling purposes and is in no part used for any other purposes, or if the assessed valuation of the property on which the tax complained of was assessed does not exceed five thousand dollars and such property is within the class of tangible personal property described in clause twentieth of section five of chapter fifty-nine, the party making the election under this section to have the complaint heard and determined by the appellate tax board shall, at the time of making such election, pay to the clerk of the county commissioners a transfer fee of two dollars. Thereupon, the clerk of the county commissioners or of the board authorized to hear and determine such complaints shall forward the transfer fee and all papers with respect to such complaint then in the files of the county commissioners or other such board to the clerk of the appellate tax board and proceedings with respect to such complaint shall thenceforth be continued as provided in chapter fifty-eight A under the formal procedure, except that complaints requiring the transfer fee of two dollars shall be continued under the informal procedure under said chapter fifty-eight A, unless the complainant files an election with the clerk of the appellate tax board that the complaint be heard under the formal procedure within ten days after receiving the notice as hereinafter provided that the complaint has been transferred to the appellate tax board. Upon the transfer of such complaint to said board the clerk of said board shall send notice by registered mail to the complainant that such complaint has been transferred, and the complainant shall, within ten days after receiving such notice, pay to said board the entry fee as required by section seven of said chapter fifty-eight A, except that the complainant shall not be required to pay any entry fee if the provisions of this section relative to the payment of the transfer fee have been complied with. Upon receipt of the entry fee or transfer fee herein provided for, the clerk of the appellate tax board shall notify the respondent board of assessors that a complaint is pending against it. In case the respondent desires to answer, it shall file an answer within thirty days of the receipt of notice of the pendency of the complaint or within such further time as the board may allow. If upon hearing it appears that the complainant has complied with all applicable provisions of law and the appellate tax board finds that the complainant is duly entitled to an abatement, it may grant him such reasonable abatement as justice may require, and shall enter an order directing the treasurer of the town to refund said amount, if the tax sought to be abated has been paid, together with all charges and interest at eight per cent on the amount of the abatement from the date of the payment of the tax. The board may make such order with respect to the payment of costs as justice may require.

If any complaint under this section is, after the period or date prescribed by this section, delivered by United States mail, or by such alternative private delivery service as the county commissioners or the board authorized to hear and determine such complaints, may permit, to the clerk of the county commissioners, or to such board, the date of the United States postmark, or other substantiating date mark permitted by the county commissioners or such board, affixed on the envelope or other appropriate wrapper in which such complaint is mailed or delivered shall be deemed to be the date of delivery, if such complaint was mailed in the United States in an envelope or such appropriate wrapper, first class postage prepaid, or delivered to such alternative private delivery service, properly addressed to the county commissioners or the board authorized to hear and determine such complaints. As used in this section, ''United States postmark'' shall mean only a postmark made by the United States post office.