What kind of mickey mouse place only sends basic delivery, or perhaps recorded, every single royal mail special delivery i have signed for, most likely this was standard first class thats the only stuff i've had that was put into a bin one time at an old student address (amazon package i think).
Being a graduation standard dress maybe it was in an envelope or bag style envelope and not immediately obvious what it was, should have just bought one from a uni shop etc and tried it on weeks before, not waiting for it to come in mail.
And if anyone thinks this guy should lose his job, stfu, these guys have to walk and deliver in all weathers thousands of items a week, should have been sent special delivery due to value, and op should have checked with sender to confirm how sent before even posting thread imo.