Never put anything in an email that you wouldn't say in public. There is no privacy on the net no matter how secure you think it is. I thought by now everyone knew that. Powell sure is full of himself. He thinks his lofty opinion is some valuable commodity. Not so much. And now, after this, not at all.
The Powell email link will not cost Clinton the presidency. However, it will further erode her honest and trustworthy numbers with Americans. It could have consequences if she is elected president - many in Congress may be too angry at her to take up any of her initiatives. Clinton will likely be elected president, because she is a Democrat, which gives her an advantage int he electoral college.
Clinton has the support of the establishment. There is nothing she can do that the media would actually seriously report on. As long as she has the following of the movers and shakers, the rest of the public will be told to just get in line. They are not even taking her health seriously. The public is not paying attention and will believe whatever the powerful people tell them to believe.
The leak of former Secretary of State Colin Powell's e-mails will help Hillary Clinton win the presidency, rather than hurt her chances. It backs up what she has been saying that Powell advised her on using a private e-mail server and he did, too. He also made disparaging remarks about her opponent, Trump, and claimed Benghazi was a witch hunt.