Starting from last week, gmail has implemented an auto list unsubscribe in the header of the email.
See illustration below:
After clicking the link, the user will then need to click to confirm you want to unsubscribe from the mailing list:
If for example, the client doesnt support this setup with gmail or the email is spam, then gmail redirects the member to navigate the clients unsubscribe or gmail policies to see the best way to be removed from the mailing list.
This might cause some uproar, but this is no showstopper in my mind. If a member doesnt want your email anyway, then better they unsubscribe directly than to complain. Look after your list and gmail will look after your reputation.