Validity of Contract sent by email - No hard copy signed

There is verbal discussion between the MD of the Pvt Ltd Co and Individual ( Consultant ) to work on consultancy assignment. Terms of engagement were discussed and then MD agreed to send the mail to consultant containing terms of engagement. 1) MD of pvt ltd co sends email to consultants mail id - is this contract / terms of engagement valid. Is email valid form of document 2) Does the consultant needs to give acceptance to the MD's mail for acceptance of terms of engagement? 3) Consultant is requesting MD to provide terms on letter head of the company and signed by MD. Is it necessary ? 4) MD replied to consultants mail saying that email is sufficient and there is no need for hard copy. In future if dispute takes place is email valid 5) As a consultant can i challenge the company on the basis of email if dispute arises 6) There has been revision in contract terms 3 times in 1 months. All terms are revised by MD and emailed to consultant 7) Is this situation part of contract act or the cyber law