Issues with sending iCloud email on Mac after El Capitan upgrade

Because apple forces users to choose an email whose domain is not owned by apple, I have to use an outdated hotmail address to sign into icloud. I normally send and receive email both from this hotmail address and my icloud address in apple's Mail application.

Since upgrading to El Capitan, I've had issues sending email from my icloud account. At first, mail which should be sent from my icloud address was sent from both my icloud and hotmail address (duplicated emails). After fiddling with some confusing settings, mail which I designate as sent from iCloud is sent from my hotmail address. I don't have this issue on my iphone, which operates as usual after upgrading to iOS 9.

My preferences in Mail says that my outgoing iCloud SMTP server is offline. I presume this is why Mail is defaulting to send from the hotmail server.

Any thoughts as to how I can get back on the iCloud server?

Thanks for the assistance. Please ask questions if I wasn't clear on certain points.

Nick