Is there a way how I can add my normal application css files (which are scss/sass) to my mailer views without duplicating code?
Didn't find a solution on the net... :/
You probably don't want to do this. Much CSS won't work in email, and so your regular CSS isn't useful in that context. As an example, in a number of clients only inline (<sometag style='attribute:value'>...</sometag>
) styles work.