That's correct - Article 27,4 of the "Vienna Convention on Diplomatic Relations":
The packages constituting the diplomatic bag must bear visible external marks of their character and may contain only diplomatic documents or articles intended for official use.
They can, but the receiving country can also kick out the ambassador and, more frequently, I believe recently some country kicked more than 10 diplomats, perhaps US against Russia.
That's correct - Article 27,4 of the "Vienna Convention on Diplomatic Relations":
The packages constituting the diplomatic bag must bear visible external marks of their character and may contain only diplomatic documents or articles intended for official use.
http://legal.un.org/ilc/texts/instruments/english/convention...