Email remains a key mode of communication between faculty and students in higher education institutions. Composing appropriate email texts is an important skill for learners; however, little technological support is available for the pragmatic aspect of email communication -- the ways in which social context influences language choices. Furthermore, pragmatics can be undertaught in the language classroom. One approach to providing support for learners while also addressing the issue of giving instruction to large class sizes is via computerisation. In this ongoing research project, we describe the development of a Computerised Diagnostic Language Assessment (C-DLA) of L2 English email writing for Japanese English as a Foreign Language (EFL) learners in Japanese higher education. The C-DLA provides automated feedback to learners on the pragmatic aspects of their draft email texts, with feedback adapting to learners' success in resolving identified issues. We report on the development phases of the project, challenges encountered, and implications for further research. [For the complete volume, "CALL and Professionalisation: Short Papers from EUROCALL 2021 (29th, Online, August 26-27, 2021)," see ED616972.]