EDIT: I've upgraded to Sierra and I'm pleased to say that the Mail issues I've had are completely fixed! I'm having serious problems with Mail in El Capitan, with the IMAP connections always timing out until I restart WiFi. This makes Mail totally useless because it can't receive emails. Has anyone had this issue in El Capitan? Did the issue get fixed in Sierra for you? Does anyone have any issues with Mail in Sierra? I'd normally hold off upgrading because who knows what problems it will cause, but if it actually fixed a problem I currently have, I may as well upgrade.