Miklos Vajna of open source consultants Collabora has produced a short video showing the recent changes in mail merge in LibreOffice.
If you ever used the mail merge wizard with a Calc data source, then you know how it worked in the past: you’ve got 3 files: the .odt mail template, the .ods data source and a .odb data source definition that defines how to access the .ods.
The procedure has now been changed. As of LibreOffice 5.1, the .odb data source has been eliminated and the .ods data source is now embedded directly the .odt mail template.