We are using Google for Work which has a global shared contact directory.
This directory by default shows all internal contacts.
It is also able to add external contacts, but unfortunately Google isn’t offering a tool for it.
There is an API for this, which could be used.
eM Client shows the directory (named “Directory”), but brings an error message “Method not supported”, when we try to add/edit contacts there.
Would be great to see support for this.