The Costa Rican postal service operates with relative efficiency and effectiveness. However, the service has been known to suffer from occasional bouts of slowness and unreliability. From time to time, mail from abroad will be opened, delayed or lost. Generally, it is best not to send anything very valuable by mail.
The main post office in San José is the Correo Central, open Monday through Saturday. Letters are better off being mailed from here than from the few available street-side mailboxes.
Because the Costa Rica customs office tries to prevent foreign merchandise from illegally entering the country, packages larger than a regular-sized envelope could be subject to high duty charges. If you receive a larger-than-ordinary package, you'll have to visit the customs office, Aduana, to have your package inspected and to pay a customs charge on each item in the package. In addition, items such as medicine or food must be examined by the Ministry of Health.
Packages sent out of the country that are larger than a regular sized envelope are checked by the Aduana, and may be permanently confiscated if they have any doubt as to the package's origin or destination.
If one is spending a significant length of time in Costa Rica, a post office box (apartado) can be rented. Having your mail sent to a box is more reliable than having it sent to a street address.