Version 2.16 of the plugin removes support for the PROJECT_DEFAULT_RECIPIENTS token, but leaves references to the token in the recipient lists for previously-configured build jobs. This causes build to attempt to send email to "$PROJECT_DEFAULT_RECIPIENTS" (literally), which of course fails. Delivery to legitimate addresses fails at the same time.

This is a breaking change, as it requires manually editing all existing jobs to remove the offending token reference. For installations with many jobs, this could be overwhelming. In general, it's not a good idea to remove functionality like this, therefore forcing your users to immediately reconfigure to use your alternate method. (i.e. the "ENV" token approach suggested in the commit comment.)

This change is also NOT listed in the version history for the plugin.

A typical failure stack trace follows.

Sending email to: real-address@mycompany.com $PROJECT_DEFAULT_RECIPIENTS
ERROR: Could not send email as a part of the post-build publishers.
javax.mail.SendFailedException: Invalid Addresses;
nested exception is:
com.sun.mail.smtp.SMTPAddressFailedException: 550 5.1.1 <$PROJECT_DEFAULT_RECIPIENTS>: Recipient address rejected: User unknown in local recipient table
at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTransport.java:1196)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:584)
at javax.mail.Transport.send0(Transport.java:169)
at javax.mail.Transport.send(Transport.java:98)
at hudson.plugins.emailext.ExtendedEmailPublisher.sendMail(ExtendedEmailPublisher.java:259)
at hudson.plugins.emailext.ExtendedEmailPublisher._perform(ExtendedEmailPublisher.java:243)
at hudson.plugins.emailext.ExtendedEmailPublisher.perform(ExtendedEmailPublisher.java:203)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:692)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:667)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:645)
at hudson.model.Build$RunnerImpl.cleanUp(Build.java:171)
at hudson.model.Run.run(Run.java:1448)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:238)