Two acts can be referred in this matter:
Section 4 and 7 of the Contract Act 1872 and further it satisfies Section 2(1)(b), 7 of the Arbitration and Conciliation Act 1996. In the absence of a signed agreement inference can be from documents approved and signed by the parties in the form of exchange emails, letters, telegrams which come within Section 10 and 2(e) of the Contract Act 1972. And also IT Act 2000 supported .
So Email Acceptance is a valid to sue legaly.