China Postal Insurance Office of Postal Bank gave an insurance policy. Is it okay if there is no red seal on the contract?

You can't. The insurance contract must be original and must be stamped with the official seal of the insurance company or the seal of the insurance agent. You received a copy of the contract, not stamped. You should contact China Post Insurance or the customer service of Postal Savings Bank in time to consult the specific situation and ask for the replacement of the original contract. Because the insurance contract is an important legal document between the insurance company and the insured, it has legal effect and needs to be guaranteed to be true and legal.