Proofpoint's URL Defense (URL Rewrite) protects you and Carthage's network resources by blocking access to malicious websites. Links in all email messages are evaluated using a variety of sophisticated techniques to determine the likelihood that they lead back to phishing or malware-infected websites.
URL rewriting modifies the links in email messages which directs you to a repository which instantly checks the URL for malicious content. If you hover over the URL you will see https://urldefense.com/v3/_ added to the beginning of the original link. If a malicious link is clicked, you will not be taken to the intended page. Instead, you will see a message stating that the web page was blocked.
How the original email message was sent to you will determine how the link appears in the email. Emails sent as 'plain-text' messages will display the rewritten URL directly in the message itself (you do not have to hover to see the rewritten URL). Emails sent in 'HTML format' will display links normally and you will only see the rewritten URL if you hover over the link. A 'plain-text' email would appear as below (notice the rewritten URL directly in the email message):