This paper investigates functional as well as structural differences and similarities between postings on two linguistic e-mail discussion lists and three other academic genres (discussion section of a scholarly journal, literature review sections of academic papers, and book reviews). The theoretical background is provided by Systemic Functional Linguistics and Fairclough’s discourse theory. In the empirical part of the paper structural and ideational theme realisations of the different genres are investigated quantitatively, transitivity and interpersonal aspects of the genres are subjected to a qualitative analysis. Results show that all genres share a common “background” which is called the “academic discourse”, but that e-mail contributions differ from all other genres with respect to several textual features including frequency of interpersonal and textual themes, as well as marked themes (prepositional phrases) etc. These results are explained as “genre mix” with oral genres in terms of Fairclough’s notion of interdiscursivity (Fairclough 1992) and Bakhtin’s concept of dialogism (Bakhtin 1981).