This trust is the relationship between the local print group and other remote groups. You can share documents between multiple Releaser servers, so a user that is in another network or have his documents stored in several servers, can release them wherever he is.
To access your documents from another network, you have to switch servers in the release agent.
To use this feature, the document retention must be performed in the server.
Environments that use local retention will not be able to use this feature.