Section 6C. Every mortgage and assignment of a mortgage presented for record shall contain or have endorsed upon it the residence and post office address of the mortgagee or assignee if said mortgagee or assignee is a natural person, or a business address, mail address or post office address of the mortgagee or assignee if the mortgagee or assignee is not a natural person. Such endorsement shall be recorded as part of the mortgage or assignment of a mortgage. Failure to comply with this section shall not affect the validity of any mortgage or assignment of a mortgage or the recording thereof. No register of deeds shall accept a mortgage or assignment of a mortgage for recording unless it is in compliance with the requirements of this section.