760 ILCS 100/21

Except as otherwise provided for in this Act, whenever the Comptroller is required to give notice to any applicant or licensee, such requirement shall be considered complied with if, within the time fixed herein, such notice is enclosed in an envelope plainly addressed to such applicant or licensee, as the case may be, United States postage fully prepaid, and deposited, registered, in the United States mail.