CONCLUSIONS OF THE OPINION: Mailboxes and channels of complaint, technical-legal aspects of mailboxes or internal channels of complaint, of the directive 1937/2019 EC. This paper explores how complaint boxes should be set up in practice, the procedure to be followed and the characteristics of the staff in charge of them.

FIRST.- The internal mailbox or channels of complaints are a complex tool, which requires a series of peculiarities for those who manage them based on the characteristics of SECURITY, INDEPENDENCE, CONFIDENTIALITY, DATA PROTECTION, SECRET and RESPONSIBILITY.

SECOND.- It is a tool that must have a series of sub-channels that must be permanently operational, web, physical letter, email, telephone and face-to-face reporting, and a series of complementary tools for the certification of communications and risk analysis.

THIRD.- It requires that the manager, investigator or administrator of the complaint channels, be apart from an INDIVIDUALIZED person (not being valid amorphous or unidentified entities), a person of high technical and legal capacities, with a very extensive knowledge of the law of the union of its obligations and of its infractions, with knowledge of the state and union administrative and criminal processes and who must advise the reporting person.

FOURTH.- that the rule imposes a term of 3 months for the procedure, which will undoubtedly include personal, documentary and expert evidence, in many cases, i.e. a real internal investigative procedure, whoever does not have such a procedure will clearly not comply with the provisions of the directive and will therefore have to be sanctioned.

FIFTH.- The channel is not only designed to filter out conflicts, but also to PROVIDE PROOF for subsequent judicial phases.

SIXTH.- The complaints channel should absorb other channels already in use, such as Bullying, Mobbing, Equality, Compliance or Mediation.

We can therefore state that not everything is valid, nor will all be valid or optimal for the design, conception and management of the channels of complaint. Self-control, that was the poor brother becomes the axis of the system.