The Vienna Convention on Diplomatic Relations and the Vienna Convention on Consular Relations are considered to be broadly reflective of customary international law. Therefore, even if a State had not ratified these Conventions, the rules analysed below would still apply to its diplomatic and consular relations.
Inviolability of documents and archives of diplomatic missions and consular posts[edit | edit source]
Diplomatic and consular law protects the inviolability of documents and archives of diplomatic missions and consular posts. This includes any official correspondence, whether in electronic or paper form. The international legal obligation to respect inviolability is unaffected by the frequent practice of States to conduct cyber espionage operations that violate this duty. This is because any such practice is regularly condemned by the victim States, whereas the offending States refrain from putting forward any corresponding legal justification of such operations.
Article 41 of the Vienna Convention on Diplomatic Relations (VCDR) provides that “it is the duty of all persons enjoying [privileges and immunities according to the Convention] to respect the laws and regulations of the receiving State”. In addition, it prohibits the premises of the mission from being used “in any manner incompatible with the functions of the mission” as these are laid down by the VCDR or in any other relevant international legal rules. In this regard, the VCDR specifically notes that legitimate functions of the mission include “[a]scertaining by all lawful means conditions and developments in the receiving State, and reporting thereon to the Government of the sending State”. This formulation thus legitimates the gathering of intelligence as long as it is conducted in a manner compatible with the domestic law of the receiving State. By contrast, most States criminalize espionage, including economic espionage, under their domestic law, and therefore conduct that falls under such domestic prohibitions will also constitute a violation of Article 41 of the VCDR.
Apart from primary rules which can be violated by the sending State’s conduct, the Vienna Convention on Diplomatic Relations also applies to the response of the receiving State. The sending State’s diplomats in the receiving State enjoy an immunity from the criminal jurisdiction of the receiving State. When they are declared personae non gratae, the sending State has to recall them or terminate their functions. Declaring personae non gratae those diplomats who were suspect of other activities against the interests of the receiving State without strong evidence is also lawful, since the receiving State's decision is fully discretionary and it does not need to provide any reasons.
The declaration as persona non grata is a specific remedy under the VCDR. However, this remedy is not the only one available; if the sending State's operation amounts to an internationally wrongful act, the receiving State could possibly invoke countermeasures in its response.
↑See, for example, J Wouters, S Duquet, and K Meuwissen, “The Vienna Conventions on Diplomatic and Consular Relations” in AF Cooper, J Heine, and R Thakur (eds), The Oxford Handbook of Modern Diplomacy (OUP 2013) 510 (noting that VCDR’s and VCCR’s main provisions have acquired customary status); ICJ, United States Diplomatic and Consular Staff in Tehran  ICJ Rep 3, 31–32  (noting that the relevant obligations under the two treaties are “also obligations under general international law”).
↑Tallinn Manual 2.0, commentary to rule 41, para. 11. However, commentary to rule 41, para. 8, notices that the Experts were divided on whether the duty to respect the inviolability over archives or material at rest on private servers as opposed to transit lies upon all States and not only the receiving State.
↑See, UK, Official Secrets Act 1911, s 1; US, 18 USC §792–799.
↑Cf. Darien Pun, ‘Rethinking Espionage in the Modern Era’ (2017) 18 Chicago JIL 353, 368; see also ICJ, United States Diplomatic and Consular Staff in Tehran  ICJ Rep 3, 39–40 – (describing espionage as an abuse of diplomatic functions under the VCDR).
↑Jean D’Aspremont, ‘Persona Non Grata’, in Rudiger Wolfrum (ed), Max Planck Encyclopedia of Public International Law (OUP 2008) (updated January 2009): “Given that the reasons need not be given by the receiving State when declaring a diplomatic or consular agent of the sending State persona non grata, the declaration of a diplomatic agent as persona non grata is utterly discretionary. The receiving State may thus make use of it for various reasons, whether for the behaviour of the agent himself or due to the actions of the sending State.”