Exchange Online Protection provides protection against malicious links by scanning content. Safe Links expands on this by protecting your environment when users click a link. While the content is being scanned, the URLs are rewritten to go through Office 365. The URLs are examined in real time, at the time a user clicks them. If a link is unsafe, the user is warned not to visit the site or informed that the site has been blocked. Reporting is available, so administrators can track which users clicked a link and when they clicked it.