Mailtrack isn't compatible with Google's Advanced Protection as to keep your data extra secure it requires the use of two security keys in order to access your Google account, which has the unfortunate side effect of preventing most non-Google apps and services (such as Mailtrack) from accessing the data they need in order to work correctly with your Google/Gmail account.
If you would like to track email opens using Mailtrack (or pretty much any other email tracking tool for that matter) you would first need to turn Advanced Protection off in your Google Account.
If you would like to track email opens using Mailtrack (or pretty much any other email tracking tool for that matter) you would first need to turn Advanced Protection off in your Google Account.