Unrelated to JENKINS-16862 I think.

Probably need to make sure that the Mailer plugin is installed and enabled.

I'm encountering the same issue with 1.512. Is the problem a master JVM vs. slave JVM issue, similar to the Groovy Plugin's System Groovy script vs. groovy script difference?...

"Groovy Script vs System Groovy Script
The plain "Groovy Script" is run in a forked JVM, on the slave where the build is run. It's the basically the same as running the "groovy" command and pass in the script.

The system groovy script, OTOH, runs inside the Hudson master's JVM. Thus it will have access to all the internal objects of Hudson, so you can use this to alter the state of Hudson. It is similar to the Jenkins Script Console functionality."
https://wiki.jenkins-ci.org/display/JENKINS/Groovy+plugin

Did you make sure that the Mailer plugin is installed and enabled?

Attached screenshot showing proof that Mailer plugin 1.4 is installed and enabled.

Here's what the failure looks like in our environment...
Groovy script failed:
groovy.lang.MissingPropertyException: No such property: hudson for class: SonarReports
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.unwrap(ScriptBytecodeAdapter.java:50)
at org.codehaus.groovy.runtime.callsite.PogoGetPropertySite.getProperty(PogoGetPropertySite.java:49)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callGroovyObjectGetProperty(AbstractCallSite.java:231)
at SonarReports.sendSuccessMail(SonarReports.groovy:158)
at SonarReports$sendSuccessMail.callCurrent(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:46)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:133)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:153)
at SonarReports.doSuccess(SonarReports.groovy:192)
at SonarReports$doSuccess.callCurrent(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:46)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:133)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:153)
at SonarReports.run(SonarReports.groovy:224)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:580)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:627)
at groovy.lang.GroovyShell$evaluate.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:42)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
at Script1.run(Script1.groovy:4)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:580)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:618)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:589)
at org.jvnet.hudson.plugins.groovypostbuild.GroovyPostbuildRecorder.perform(GroovyPostbuildRecorder.java:276)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:802)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:774)
at hudson.maven.MavenModuleSetBuild$MavenModuleSetBuildExecution.post2(MavenModuleSetBuild.java:949)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:724)
at hudson.model.Run.execute(Run.java:1600)
at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:477)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:237)

Can you post your groovy script? This looks like a different failure than described in this issue.

Attaching the SonarReports.groovy script run by the Groovy Post-Build action plugin (https://wiki.jenkins-ci.org/display/JENKINS/Groovy+Postbuild+Plugin). Execution of this script fails when line # 158 is executed

mailSession = hudson.tasks.Mailer.descriptor().createSession()

A fix for this groovy post-build defect might be similar to the fix JENKINS-6068 applied for the Groovy plugin defect JENKINS-14154.

At least JENKINS-6068 suggests a possible workaround that involves doing something like
Class.forName("hudson.tasks.Mailer", true, manager.hudson.getPluginManager().uberClassLoader)

Where the manager.hudson identifier in the "manager.hudson.getPluginManager().uberClassLoader" part is the hudson instance owned by the manager variable. The groovy post-build action plugin binds this variable for script use.

After applying the uberClassLoader workaround, the Groovy post-build action script succeeds.

The same root cause to JENKINS-14154.