Jenkins Mail Failure

Sending e-mails to: <email address hidden>
ERROR: 501 Syntactically invalid HELO argument(s)

javax.mail.MessagingException: 501 Syntactically invalid HELO argument(s)

 at com.sun.mail.smtp.SMTPTransport.issueCommand(SMTPTransport.java:1363)
 at com.sun.mail.smtp.SMTPTransport.helo(SMTPTransport.java:838)
 at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:375)
 at javax.mail.Service.connect(Service.java:275)
 at javax.mail.Service.connect(Service.java:156)
 at javax.mail.Service.connect(Service.java:105)
 at javax.mail.Transport.send0(Transport.java:168)
 at javax.mail.Transport.send(Transport.java:98)
 at hudson.tasks.MailSender.execute(MailSender.java:110)
 at hudson.tasks.Mailer.perform(Mailer.java:101)
 at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
 at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:662)
 at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:638)
 at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:616)
 at hudson.model.Build$RunnerImpl.post2(Build.java:161)
 at hudson.model.AbstractBuild$AbstractRunner.post(AbstractBuild.java:585)
 at hudson.model.Run.run(Run.java:1398)
 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
 at hudson.model.ResourceController.execute(ResourceController.java:88)
 at hudson.model.Executor.run(Executor.java:145)
Notifying upstream projects of job completion
Finished: FAILURE