Ключевые слова: address, airmail, anniversary, belgian, belgian flag, belgium, belgium flag, bill, brussels, business, card, celebration, communication, concept, congratulation, copy space, correspondence, delivery, design, document, email, envelope, exchange, greeting, holding, investment, invitation, letter, letter of happiness, mail, mailing, message, modern, national, national holiday, nationality, notebook, paper, payment, pen, pictogram, post, post office, postage, postcard, registration, retro postage, symbol,