The sender of the email, would likely have a setup behind him. To even inititate legal proceedings would not be easy, if non-Islamic forces are involved.
First info-warefare needs to be overcomed, which would involved denigeration, hood-winking, subterfuge and offensive propaganda of severe proportion, far more than what India can bear. The initial effort would be to nip it in the bud.
The first few steps need to be diplomatic. First disenegage from an active initiatives being undertaken.
Provide adequate time for Indian economic leaders upto middle level to take suitable measures to prepare for the inevitable counter measures which would be applied on India.
Legal stepsto be effective ought to work on fidility to sanctity of India with no scope for any negotiation and full scope subjection to Indian law of all guilty persons.
The series of measures required to be able to lift the issue, step by step to a level commensurate with the counter measures which would have already been thought out shall not be easy.
Onw hopes that such an outcome never arises, but need to be prepared is also important. The fuzzy feelings associated with the outcome is not positive. And it is time the guilty ones be made to pay the cost of their crimes.