Step 1: Apply Section 4 of the Contract Act.
Communication of acceptance is complete against the proposer when the acceptance is put into a course of transmission, beyond the acceptor's control.
Step 2: Meaning.
Once the acceptor posts, emails, or sends the acceptance such that he cannot revoke it, the proposer becomes bound.
Step 3: Conclusion.
Thus, communication is complete when acceptance is dispatched beyond the acceptor’s control.