Communicating with IT is absolutely part of the onboarding process. And the phrasing of the email clearly states they are rescinding an offer acceptance, as in they had already accepted and begun onboarding.
You are not considered to be working somewhere until you have signed a contract and after the start date on that contract. Accepting a offer is not signing a contract. You are not working at the new place yet. You have no obligations to do anything at that point. You just need to have stopped working at your current employment before your start date. You definitely do not need to quit before accepting the offer. No where I have worked requires that.
Communicating with IT is absolutely part of the onboarding process. And the phrasing of the email clearly states they are rescinding an offer acceptance, as in they had already accepted and begun onboarding.
You are not considered to be working somewhere until you have signed a contract and after the start date on that contract. Accepting a offer is not signing a contract. You are not working at the new place yet. You have no obligations to do anything at that point. You just need to have stopped working at your current employment before your start date. You definitely do not need to quit before accepting the offer. No where I have worked requires that.