Regarding Tourist Information center located inside Post Office - beware young boy is trying to scam under flag of Tourist Information. Not good for flagship post office building in Mongolian capital.
Good service
They talk English
Easy to send international packages
Mostly suitable for sending cargos and letters
Somehow they charge you 10% tax on the stamps they sell... .
Helpful and opened every day from 8 to 8. poste restante is possible
Once in while they sell cool stamps :)