It all falls under the same legal concept and the rule of law as it says that under certain circumstances you have to sign the contract or else it is not a valid contract. If it was never approved, then it is not binding or valid. If you're a recruiter and you don't have a signed contract, then, you don't have a case.
An oral contract cannot be longer than one year, because if you do, that's more likely do not having a contract at all. But, an email or an acceptance of a resume could be connected to your contract, by following an attorney's legal advice.
It doesn't mean that the acceptance of an email or the approval of a resume means that you accept the terms and conditions. It gives an argumentative point and not absolute unless you bind it to your written contract and have it signed.
