Evidence Act vs BSA: Admissibility of Unsigned Email

Rohan, an employee of ABC Inc, sends an angry email to his manager, Kumar, but forgets to sign it. The email contains damaging accusations against Kumar and his business partner, Rohit. Later, when a police officer asks Rohan if he sent the email, Rohan denies it, citing the fact that he didn't sign it. The police officer, having obtained an IP address of the sender, confronts Kumar with the email. Kumar demands an investigation into the malicious accusations. What legal remedy applies in this scenario?