pipeline {
    agent any
    stages {
        stage('one') {
            agent any
            steps {
                script {
                    println 'Hello world'
                }
            }
        }
    }
    post {
        always {
            println 'xxxxxxxxxxxxxxxxxxxxxxxxxx'    
            emailext body: """
    		    <p><b>Build Initiated by test</b> </p>
                <p>${DEFAULT_CONTENT}</p>
                <p></p>
                <p><a href="HOST">HOST</a></p>
        """,
            subject: '$DEFAULT_SUBJECT',
            to: "srb@gmail.com"
        }
    }
}

groovy.lang.MissingPropertyException: No such property: DEFAULT_CONTENT for class: WorkflowScript
	at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.unwrap(ScriptBytecodeAdapter.java:53)
	at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.getProperty(ScriptBytecodeAdapter.java:458)
	at org.kohsuke.groovy.sandbox.impl.Checker$6.call(Checker.java:290)
	at org.kohsuke.groovy.sandbox.GroovyInterceptor.onGetProperty(GroovyInterceptor.java:68)
	at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onGetProperty(SandboxInterceptor.java:348)
	at org.kohsuke.groovy.sandbox.impl.Checker$6.call(Checker.java:288)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:292)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:268)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:268)
	at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.getProperty(SandboxInvoker.java:29)
	at com.cloudbees.groovy.cps.impl.PropertyAccessBlock.rawGet(PropertyAccessBlock.java:20)
	at WorkflowScript.run(WorkflowScript:30)