Hide email address from bots without using scripts and maintain mailto: functionality. Method must also support screen-readers.
First, I don't think doing anything with CSS will work. All bots (except Google's crawler) simply ignore all styling on websites. Any solution has to work with JS or server-side.
A server-side solution could be making an that links to a new tab, which simply redirects to the desired mailto:
That's all my ideas for now. Hope it helps.