The phrase "official notification" refers to a formal communication or message sent by an official authority to inform someone about an important matter or decision. Full definition
3.1.1 A person shall be eligible for membership in the CATA upon receipt of official notification of membership from the National Athletic Trainer's Association, Inc. national office. (ctathletictrainers.org)
We received official notification of our 501 (c)(3) status with the IRS on May 13, 2004. (caninecancerawareness.org)
I received official notification from Wattpad Management that I was now one of the most followed authors on Wattpad and even being nominated to be a judge on prizes. (writing.ie)