The Joint Declaration was agreed upon at an informal meeting of the European Chiefs of Police in London hosted by the National Crime Agency on 18 April.
Police Chiefs of all EU Member States and Schengen Associated Countries were invited, alongside Europol’s Executive Director.
Here is the declaration (pdf).
You don’t even have to go so far.
Several European countries consider physical letters to be confidential.
https://en.wikipedia.org/wiki/Secrecy_of_correspondence
Strangely enough that confidentiality suddenly no longer applies to other, “newer” forms of communication.
Probably because it’s less easy for security services to ignore.