Legal analysis: The house purchase contract becomes effective when signed by mail. Whether the contract is effective or not is directly related to whether the content of the contract violates the mandatory provisions of the law and whether the subject of the contract has truly expressed his will. It has nothing to do with the form of signature. In principle, as long as it is signed by the person himself, and It doesn't matter whether you send it by mail or not. If the home purchaser is indeed unable to sign due to special circumstances, he may entrust another adult citizen in writing to act as his agent.

Legal basis: Article 502 of the "People's Republic of China and Civil Code" A contract established in accordance with the law shall take effect from the time of establishment, unless otherwise provided by law or otherwise agreed by the parties. In accordance with the provisions of laws and administrative regulations, if the contract should be subject to approval and other procedures, the provisions shall be followed. If the failure to go through approval and other procedures affects the effectiveness of the contract, it will not affect the effectiveness of the contract's obligations such as reporting for approval and the effectiveness of related clauses. If the party that should go through the application approval and other procedures fails to perform its obligations, the other party may request that it bear liability for violating such obligations. In accordance with the provisions of laws and administrative regulations, if the modification, transfer, termination, etc. of a contract require approval and other procedures, the provisions of the preceding paragraph shall apply.