As for EMS, size and weight restrictions vary depending on the country/region of destination.
Example) Bulgaria: Up to 20kg.
If it is 20kg or more, an error message will be displayed.
For more details, please check the Japan Post page.
Also, when you create EMS labels, a set of necessary documents for the desitination country will be issued. The required documents vary depending on the country of destination. Please refer to the Japan Post page for the full list.