Section 16. The collector shall, before selling the land of a resident, or non-resident, or distraining the goods of any person, or arresting him for his tax, serve on him a statement of the amount thereof with a demand for its payment. If two or more parcels of land are assessed in the name of a resident, or non-resident, the statement of the aggregate amount of the taxes thereon may be made in one demand. Such demand may also include taxes due on account of tangible personal property and any motor vehicle excise tax. If the heirs of a deceased person, co-partners or two or more persons are jointly assessed, service need be made on only one of them. Such demand for the tax upon land may be made upon the person occupying the same on January first of the year in which the tax is assessed. No demand need be made on a mortgagee, unless he has given notice under section thirty-eight, in which case no demand need be made on the owner or occupant. Demand shall be made by the collector by mailing the same to the last or usual place of business or abode, or to the address best known to him, and failure to receive the same shall not invalidate a tax or any proceedings for the enforcement or collection of the same.