You have given three levels for breaking up training module on "Business Writing Skills". However, considering the corporate environment in which the software professionals work, I feel that this trifurcation may not be needed. Keep one single module and let everybody learn it.
As far as pre-training is concerned, lot of material is available on the web. They can very well read it and come prepared. You prepare the test exercises and begin the training with exercises. Later have the discussion. I feel that this method will help in imbibing the basics of e-mail etiquette.
For your training, you may include the following topics:
a) Difference between spoken language and written language
b) Where informal language should end and where formal language should start
c) Choice of words for the Subject Heading
d) How to avoid mismatch between Subject Heading and Main body of the mail
e) Difference between mail that is written to customers and for internal staff members
f) E-mail to very senior officials like Directors
g) Structure of the mail (most important) including rules of attachment
h) When not to use e-mail
Feedback on your post: - I do not know whether you will conduct the training on e-mail writing or someone else will. Nevertheless, there is scope to improve the quality of your post. If you are going to conduct the training then your post does not reflect your expertise in the subject. Neither you have given proper introduction nor have you signed off your post properly. You could have avoided wordiness in the subject heading. Added to this were 1-2 grammatical mistakes. A trainer is a trainer provided he/she is head and shoulder above the participants!
All the best!
31st August 2015 From India, Bangalore