Maybe a bug~smtp server can't be change~

I refer to this discuess page.

https://discussions.apple.com/thread/3377126?answerId=16350158022#16350158022

I guess I got the same problem. When I sent the mail, I got the system messenge to ask me setup up the server. However, when I setuped up my mail box's primary smtp address I got the other problem. I can't toggle "DONE" this button. It's grey out.

I wish Apple can have a fix update for this issues. It suppose not only one having this problem.