What is DTF-998.9

Does anyone know what Department of Taxation & Finance letter 998.9 is?  It was supposed to be delivered Certified mail on Friday but since I am in a building the mailman doesn't come up.  Now I have to pick it up at the post office on Monday.  I am going out of my mind because I haven't gotten any letters froom them so why a Certified mail.  It does say audit division on the envelope.