For the public postal service, you’ll find a postal service center in almost every city and town in Costa Rica. San Jose is the main hub where most of the packages from abroad get directly sent. So the farther you are from San Jose the longer the waiting time, although delivery to areas in like Jaco Beach and the Central Pacific are just usually one day longer.
Is it safe to send packages through the public mailing system? Yes, it is. By adding a small fee, you can also require the receiver to sign a document upon pickup, giving you the assurance that the package has already been sent.
You can also use Fedex or DHL if the package is that important. At least through these services, you’ll be assured that everything is sent safely.