Have a look, to these reference to find more information about this:
Emmerson, P. (2003). Email english Macmillan Education.
Stickler, U., & Lewis, T. (2008). Collaborative lenguage learning strategies in an email tandem exchange. En S. Hurd, & T. Lewis (Eds.), Language learning strategies in independent settings (1st ed., pp. 237-261). Bristol, UK: Multilingual Matters.
Vinagre, M. (2005). Fostering language learning via email: An english – spanish exchange. Computer Assisted Language Learning, 18(5), 369.
Email writing http://www.teachingenglish.org.uk/try/lesson-plans/email-writing
Good luck with your exams!