What is the exception Under Civil Code of the California if a carrier withhold delivery of a shipment?

Answer 1

That all depends upon what is being shipped. Explosives of any kind are prohibited without special permits, Guns may not be sent through the mail etc. A more specific question will result in a more specific answer.

Answer 2

Your question needs more detail. It may depend on why they are withholding delivery. Did whoever sent the item require obtaining the signature of a specific person on delivery? If so, was that person available to sign. Perhaps the item was shipped COD (cash on delivery). In that case, they can withhold delivery until they are paid.