Important documents dropped in letter box always

I have our office at gala no.7.8.107 & 108,samayak,sagar plaza indl. Estate, boidapada, sativali, vasai (e) - 401 208 having regular business with you. I always get the letters / Samples at branch off. At swapna,flat no.20, 5-26 rambaug colony, kothrud, pune - 411 038. My letters / Sample always dropped in letter box. Who is accepting this letters, signing. Please clarify immediately. Recent docket no. 9369 dt. 8.12 is dropped in my letter box on .12. How many it require to come. I always get letters after 5 -6 days.