Hi there. If i were in your position, certain degree of professionalism still has to be maintained. It shows your quality in character. You may not need to blast email to tell everyone you're leaving now (I mean now, not your last day). But as formality, it is proper to send an appreciation email to relevant co-workers during the last day. Unless they did you a serious offense, otherwise it is best to remain certain degree of professionalism, for Richard L. Evans once said "Don't let life discourage you; everyone who got where he is had to begin where he was". All the best to your new endeavour!