In all cities having a population of more than six hundred thousand inhabitants, as shown by the last United States census, no notice or other advertisement permitted or required by law to be made in conformity with the power of sale of real estate contained in any mortgage or deed of trust shall be valid or sufficient unless such notice or other advertisement shall be published in a daily newspaper, published in such city, whose annual cash receipts from circulation shall exceed six thousand dollars; and such receipts shall be paid by the bona fide individual and separate subscribers of such newspapers in such city, and in computing such receipts there shall not be counted or included cash received from advertising or from any other source.