All of our email goes through Proofpoint. It has a feature that redirects all links to their URL Defense before allowing it to continue to the original destination. However, when the link is typed out in the email, Thunderbird pops up with the message that there is a Link Mismatch Detected and it lets the user go to the actual link instead of forcing it through the Proofpoint URL Defense. I need to disable that feature or create an exception for anything that redirects to Proofpoints URL.