(a) All applications for membership, retirement, optional selections, loans, refunds, military service credit, prior service credit, transfer, and designation of beneficiary shall be made on appropriate forms to be furnished by the system and must be received at the system's office to be effective. Provided, however, whenever a statute requires that a document must be filed or moneys deposited with the system within a prescribed period of time or by a specified date in order for a member to be eligible for service credit or a benefit from the system, the document shall be deemed filed or the moneys deposited with the system on the day they are mailed through the United States Postal Service provided the mailing is by registered or certified mail. Notwithstanding these provisions, no such document shall be deemed filed or moneys deposited with the system on the day of mailing unless actually received by the system as a result of such mailing.

(b) All regularly employed (on a per annum basis) full-time teachers, as provided in subdivision 4 of section 501 of the Education Law, shall be required to become members of the system.

(c) Membership in the system, as set forth in subdivision (b) of this section, shall become effective when full-time employment commences whether or not application for membership is made.

(d) Membership shall be optional on an individual basis for any class of teachers, as provided in subdivision 4 of section 501 of the Education Law, whose compensation is only partly paid by the employer or who are serving on a temporary or any other than a per annum basis.

(e) Commencing July 1, 2004, membership which is optional pursuant to subdivision (d) of this section shall commence on the earlier of:

(f) Notwithstanding any provision of this plan to the contrary, contributions, benefits and service credit with respect to qualified military service will be provided in accordance with section 414(u) of the Internal Revenue Code of 1986, as amended. Effective for deaths occurring on or after January 1, 2007, if a member dies while performing qualified military service as defined in section 414(u) of the Internal Revenue Code of 1986, the survivors of the member shall be entitled to any additional benefits as determined under section 401(a)(37) of the Internal Revenue Code of 1986 provided under the system had the member resumed his or her prior employment with an employer that maintains the system and then terminated employment on account of death, and service for vesting purposes shall be credited to such deceased member for the period of his or her qualified military service. For purposes of this subdivision, the term additional benefits shall not include benefit accruals relating to the period of qualified military service.

(g) Commencing July 1, 2013, employee contributions for a tier 6 member who has been granted a retroactive mandatory membership shall have the rate of contribution determined by the actual wages earned by such tier 6 member during the plan years affected by the mandatory membership.

(h) The system intends to satisfy section 401(a) of the Internal Revenue Code by meeting the requirements of section 414(d) of the Internal Revenue Code relating to the establishment of retirement plans for governmental employees of a State or political subdivision thereof.

(i) Notwithstanding any other provision of law, no funds of the system shall be expended for any purpose other than the expense of administration of the system, investments for the benefit of the system, and the provision of benefits to the members and retired members of the system and their survivors and beneficiaries; provided, however, that reversions will be permitted only to the extent allowed under the Internal Revenue Code and any related guidance thereunder, including, but not limited to, a mistake of fact as permitted under Internal Revenue Ruling 91-4, or other applicable guidance.