Jenkins file code to send email notification on error

I need to run my test project in TestComplete14 every night, and I need to be able to send result (Succeeded/Error(s) occurred) as a part of a email subject.
Currently, I run the test project in Jenkins as a scheduled nightly job and also use Jenkins file to send email notification for pass/fail build status .I want to go a step further and code Jenkins file to send email notification of Success if all test cases passed and Fail if there is given percentage of errors. I am having trouble to accomplish that. Can anyone help?

Below is the Jenkins file code, which I use currently for email notification for Build status -

post {

        always {

            echo "Notifying build result by email"

        }

        success {

            mail to: 'email address',

                 subject: "SUCCESS: ${currentBuild.fullDisplayName}",

                 body: "Test Complete Build passed."

        }

        failure {

           mail to: 'email address',

                subject:"FAILURE: ${currentBuild.fullDisplayName}",

                body: "Test Complete Build failed."

        }