(1) Beneficial associations which are formed by or for the exclusive benefit of those who, at the time of becoming members of such associations, are engaged in educational work in any department or district of the public school system of the Commonwealth of Pennsylvania, or in any college or university therein, and which issues beneficiary certificates only to such members.

(2) Fraternal, charitable or secret societies issuing beneficial certificates and paying benefits to their membership through the lodge system.

(3) Insurance or relief associations formed by or for the exclusive benefit of employes of corporations or firms, or formed by or for the exclusive benefit of members of any religious corporation or association.

(4) Associations whose benefits are limited to post-mortem assessments of the members.