Reply #2: Personally...

[Chan790]

I'd probably just send it to the chair (and second if there is one); verbally inform the rest personally, making a point to tell them how much you enjoyed working with them (personally) and thanking them for the opportunity. (even if you hated your job and they abused you terribly and you think they're all assholes who should be used to test weaponized smallpox.)

Make sure you're giving sufficient notice, many such organizations consider it two weeks from the meeting where the resignation is formally acknowledged & not two weeks from when you gave the letter to the chair.

It's all about getting great references and connections on your way out the door.