this could have multiple causes.
1: Something in your email settings changed (in this case we need to know what kind of email service you're using).
2: Something in IE changed. E.g. Security Settings (Got to Tools - Internet Options)
3: Your Anti-virus security settings changed. Or if it is only one link, it may contain dangerous contents or lead to an infected web page and that's why your Anti-virus doesn't let you open the page.
Hope you'll find the solution.