Does Mail on OS X mark mail as read on the server or just locally? Back when I used the Mail app on Leopard and Snow Leopard, it never seemed to tell the Gmail server that to mark as read the messages that I read. This had the annoying effect of requiring me to go to my web browser and mark everything as read there. 

Needless to say, I didn't use it much since I would have to go to my web browser to mark it as read anyway.

Does the Mail app in El Captain have this problem? (I switched back to Windows a while back)

EDIT: I want to clarify that I want Mail to automatically mark messages as read as I read them, without having to do anything else. You know, how it normally works with every other email app.
Mail in OS X El Capitan doesn't have this problem. 

Mark as Read &amp; Mark as Unread affect all of the devices linked to your IMAP account.