205 ILCS 405/21

Except as otherwise provided for in this Act, whenever the Secretary is required to give notice to any applicant or licensee, such requirement shall be complied with if, within the time fixed herein, such notice shall be enclosed in an envelope plainly addressed to such applicant or licensee, as the case may be, at the address set forth in the application or licensee's principal office, as the case may be, United States postage fully prepaid, and deposited, registered or certified, in the United States mail.

Notice may also be provided to an applicant or licensee by telephone facsimile to the person or electronically via email to the telephone number or email address designated by an applicant or licensee in writing.