In Inbox Preview, Content Assessment is a feature that offers a general overview as well as a detailed look into the performance of your test email's links, which is called Link Check. Link Check uses Google Safe Browsing to check your links against Google's updated lists of suspected phishing, malware, and unwanted software pages. 

Available Link Check information includes:

• Valid Link: Shows whether a link is valid or broken and offers a status report
• Safe Link: Shows whether a link is safe or unsafe
• Click Tracking: Shows whether a link has click tracking enabled or disabled 
• Preview: Shows a preview of the link, if available