LibreOffice Writer was always capable of mass-sending mail using mail merge, but setting it up is far from easy. One obstackle there is having to create three different documents: a Writer one, a Base data source and e.g. a Calc document containing the real data. LibreOffice 5.1 has a new feature to allow embedding the data source definition into a Writer document, meaning you can get along with e.g. a Writer and a Calc document. Come and see how it's implemented, where are the still rough edges and how you can help.