Hi
Sorry for the latest reply. The issue is still a problem.
In order to reproduce it, you need to configure an empty job with extended email configuration and to enter email address in the success recipient list (but leave the global recipient list empty).
Here is the exception that appears in the console output of the job:
Email was triggered for: Success
There are 1 triggered emails.
Sending email for trigger: Success
ERROR: Could not send email as a part of the post-build publishers.
javax.mail.internet.AddressException: Illegal address in string ``''
at javax.mail.internet.InternetAddress.<init>(InternetAddress.java:94)
at hudson.plugins.emailext.ExtendedEmailPublisher.createMail(ExtendedEmailPublisher.java:287)
at hudson.plugins.emailext.ExtendedEmailPublisher.sendMail(ExtendedEmailPublisher.java:249)
at hudson.plugins.emailext.ExtendedEmailPublisher._perform(ExtendedEmailPublisher.java:241)
at hudson.plugins.emailext.ExtendedEmailPublisher.perform(ExtendedEmailPublisher.java:199)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:541)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildStep(AbstractBuild.java:527)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildStep(AbstractBuild.java:515)
at hudson.model.Build$RunnerImpl.cleanUp(Build.java:158)
at hudson.model.Run.run(Run.java:1218)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:123)
P.S. I forget to mention that no email has been sent 
Created an attachment (id=216)
This is a fixed version of the email publisher. The changes are on line 204 (adding the check for empty list) and line 183(printing the exception, otherwise the user will never understand what the problem is)