Overview:

Approved email links and buttons return an error page with a VPN connection: This Site Can’t Be Reached.

Root Cause:

The Approved Email processing is the following:

1. The MultiChannel server prepares the emails with the original HTTPS links.
2. Mailgun masquerades the links with HTTP prefix for tracking.
3. After the emails leave Mailgun, the process is out of Veeva's control.
4. When the end-user opens the email with the remote images or clicks on the links, the HTTP requests return to Mailgun where they are translated back to the original HTTPS links.
5. If a VPN client blocks HTTP traffic, the masqueraded links do not work as expected (nothing received by Mailgun like in this case).
   
   When the end-user does not use a VPN client, everything works fine (even with Outlook). Nothing blocks HTTP traffic and Mailgun can return the response with the original HTTPS links.

Solution: