Sending a package abroad generally takes less time and costs start around $35 USD for a small package no heavier than 2 kg that can enter the mailbox and approximately $2 USD for a post card.
All international mail addressed to Quito arrives at the main mail office near Carolina Park, address: Japon N36-153 y Naciones Unidas. In case your mail from abroad did not arrive after one month, it is worth going there to check. Although addresses do have postal codes, it is not necessary to mention them on the envelope, since they are not used. The correct way to address an envelope:
Maria Sanchez
Japon N36-153 y Naciones Unidas
Quito, Ecuador
Quito and its valleys have around 20 national post offices. The closest office, and their services, you can you find on the official website.