If you have set the connection data for d.ecs domino on the HCL Domino server, you also have to set the connection data in d.3one for the connection between the d.3one application server and d.ecs domino.
This is how it works
Open the Configuration feature from the start page and navigate to E-mails in the Document management category.
Select the entry IBM Domino under E-mail management.
Select Enable IBM Domino services.
Under d.ecs domino service server, enter the host name of the client PC where d.ecs domino is installed.
Under d.ecs domino service port, enter the port for d.ecs domino. The default port is 8182.
Save your entries and restart the Groupware app.