In the past (say, with Snow Leopard, although I don't remember exactly when I set up my old client) it used to be possible to have a "one-way synchronization" between the Mail client and a gmail account in the following sense: the Mail client would download any new messages that were sent to my email, but would not notify gmail of any changes that I made locally.
The main advantage of this setup is that I could have an unofficial "cloud storage": my local client would be where I actually did my work. It would contain the emails I actually needed to respond to, and my drafts, etc. But I could recklessly delete things locally with the knowledge that if I ever really needed them, even years later, I just had to log into my account online.
Is there any way to do this with El Capitan? or at least to simulate the effect somehow?