For composing messages of a particular type, layout instructions identical for each document are provided. In accordance with selection instructions, in each case, for a prescribed position in the documents, data are selected and read from a data source. In accordance with layout instructions, the read data are processed into documents. In accordance with the handling instructions, the read data are processed into message data (19, 20, 21, 22, 23) other than the document data. The finishing of the documents into messages is done in accordance with the message data. A system and a computer program for practicing the proposed method is also described.