I've also encountered this issue, still unfixed as of Jenkins 1.433. Here is log output (tweaked to hide the innocent); the address c@test.com really wasn't a valid address, but it was picked up as submitter "c" in a SCM change.
23:35:15 Email was triggered for: Failure
23:35:15 Sending email for trigger: Failure
23:35:15 Sending email to: j@test.com s@test.com c@test.com viraghu@test.com
23:35:16 ERROR: Could not send email as a part of the post-build publishers.
23:35:16 javax.mail.SendFailedException: Invalid Addresses;
23:35:16 nested exception is:
23:35:16 com.sun.mail.smtp.SMTPAddressFailedException: 550 5.1.1 <c@test.com>... User unknown
23:35:16
23:35:16 at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTransport.java:1196)
23:35:16 at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:584)
23:35:16 at javax.mail.Transport.send0(Transport.java:169)
23:35:16 at javax.mail.Transport.send(Transport.java:98)
23:35:16 at hudson.plugins.emailext.ExtendedEmailPublisher.sendMail(ExtendedEmailPublisher.java:243)
23:35:16 at hudson.plugins.emailext.ExtendedEmailPublisher._perform(ExtendedEmailPublisher.java:227)
23:35:16 at hudson.plugins.emailext.ExtendedEmailPublisher.perform(ExtendedEmailPublisher.java:189)
23:35:16 at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
23:35:16 at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:693)
23:35:16 at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:668)
23:35:16 at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:646)
23:35:16 at hudson.model.Build$RunnerImpl.cleanUp(Build.java:171)
23:35:16 at hudson.model.Run.run(Run.java:1447)
23:35:16 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
23:35:16 at hudson.model.ResourceController.execute(ResourceController.java:88)
23:35:16 at hudson.model.Executor.run(Executor.java:230)
23:35:16 Caused by: com.sun.mail.smtp.SMTPAddressFailedException: 550 5.1.1 <c@test.com>... User unknown
23:35:16
23:35:16 at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTransport.java:1047)
23:35:16 ... 15 more
23:35:16 Notifying upstream projects of job completion
23:35:16 Finished: FAILURE
I've also encountered this issue, still unfixed as of Jenkins 1.433. Here is log output (tweaked to hide the innocent); the address c@test.com really wasn't a valid address, but it was picked up as submitter "c" in a SCM change.
23:35:15 Email was triggered for: Failure
23:35:15 Sending email for trigger: Failure
23:35:15 Sending email to: j@test.com s@test.com c@test.com viraghu@test.com
23:35:16 ERROR: Could not send email as a part of the post-build publishers.
23:35:16 javax.mail.SendFailedException: Invalid Addresses;
23:35:16 nested exception is:
23:35:16 com.sun.mail.smtp.SMTPAddressFailedException: 550 5.1.1 <c@test.com>... User unknown
23:35:16
23:35:16 at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTransport.java:1196)
23:35:16 at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:584)
23:35:16 at javax.mail.Transport.send0(Transport.java:169)
23:35:16 at javax.mail.Transport.send(Transport.java:98)
23:35:16 at hudson.plugins.emailext.ExtendedEmailPublisher.sendMail(ExtendedEmailPublisher.java:243)
23:35:16 at hudson.plugins.emailext.ExtendedEmailPublisher._perform(ExtendedEmailPublisher.java:227)
23:35:16 at hudson.plugins.emailext.ExtendedEmailPublisher.perform(ExtendedEmailPublisher.java:189)
23:35:16 at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
23:35:16 at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:693)
23:35:16 at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:668)
23:35:16 at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:646)
23:35:16 at hudson.model.Build$RunnerImpl.cleanUp(Build.java:171)
23:35:16 at hudson.model.Run.run(Run.java:1447)
23:35:16 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
23:35:16 at hudson.model.ResourceController.execute(ResourceController.java:88)
23:35:16 at hudson.model.Executor.run(Executor.java:230)
23:35:16 Caused by: com.sun.mail.smtp.SMTPAddressFailedException: 550 5.1.1 <c@test.com>... User unknown
23:35:16
23:35:16 at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTransport.java:1047)
23:35:16 ... 15 more
23:35:16 Notifying upstream projects of job completion
23:35:16 Finished: FAILURE