Send a mail from Jenkins in Groovy Script Console

sendMail.groovy

import javax.mail.Session
import javax.mail.Message
import javax.mail.Transport
import javax.mail.internet.MimeMessage
import javax.mail.internet.InternetAddress


def descriptor = Jenkins.instance.getDescriptor("hudson.tasks.Mailer")

Session session = descriptor.createSession();
MimeMessage msg = new MimeMessage(session);

InternetAddress fromAddress = new InternetAddress(descriptor.getAdminAddress());

msg.setFrom(fromAddress)

msg.setRecipients(MimeMessage.RecipientType.TO, (InternetAddress[]) [new InternetAddress('anders.sigfridsson@gmail.com')].toArray());

String charset = descriptor.getCharset();
msg.setSubject("Test", charset);
msg.setText("Hello from Jenkins!", charset)

Transport transporter = session.getTransport("smtp");
transporter.connect();
transporter.send(msg);

Hi,
I am getting this error could you please help:
org.jenkinsci.plugins.scriptsecurity.sandbox.RejectedAccessException: No such field found: field java.lang.Class TO
17:23:33 at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.unclassifiedField(SandboxInterceptor.java:419)
17:23:33 at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onGetProperty(SandboxInterceptor.java:403)
17:23:33 at org.kohsuke.groovy.sandbox.impl.Checker$6.call(Checker.java:288)
17:23:33 at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:292)
17:23:33 at org.kohsuke.groovy.sandbox.impl.Checker$checkedGetProperty.callStatic(Unknown Source)
17:23:33 at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallStatic(CallSiteArray.java:56)
17:23:33 at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:194)
17:23:33 at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:230)
17:23:33 at Script1.run(Script1.groovy:40)
17:23:33 at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.GroovySandbox.run(GroovySandbox.java:154)
17:23:33 at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript.evaluate(SecureGroovyScript.java:340)
17:23:33 at hudson.plugins.groovy.SystemGroovy.run(SystemGroovy.java:95)
17:23:33 at hudson.plugins.groovy.SystemGroovy.perform(SystemGroovy.java:59)
17:23:33 at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
17:23:33 at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:744)
17:23:33 at hudson.model.Build$BuildExecution.build(Build.java:206)
17:23:33 at hudson.model.Build$BuildExecution.doRun(Build.java:163)
17:23:33 at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:504)
17:23:33 at hudson.model.Run.execute(Run.java:1810)
17:23:33 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
17:23:33 at hudson.model.ResourceController.execute(ResourceController.java:97)
17:23:33 at hudson.model.Executor.run(Executor.java:429)

When i am using this script direct from execute system groovy command or from script console it works!
But when i put it to Config File Management and use this groovy file on job, it fails.