Tracked links in emails resolve to "Your connection is not private", or other security warnings in the browser, when clicked.
The browser is expecting the branded link domain to be secured with a SSL certificate.
Subscriptions without Secured Domains for Tracking Links: Please contact your Customer Success Manager to discuss purchasing a subscription to Secured Domains for Tracking Links.
Subscriptions with Secured Domains for Tracking Links: Please contact Marketo Support to provision a SSL certificate onto your tracking link domain. More information can be found here https://nation.marketo.com/docs/DOC-6231-overview-faq-secured-domains-for-tracking-links