Oh, good. Another one I can't replicate...

Do you have the Mailer plugin enabled?

Yes, Mailer is enabled. I guess that means I should disable it?

No, it should be enabled. Let me look into it some more.

There is a later error but I assume that is unrelated:

May 14, 2015 12:26:52 PM WARNING hudson.plugins.active_directory.ActiveDirectoryUnixAuthenticationProvider retrieveUser
Credential exception trying to authenticate against uktm.eu.nec.com domain
org.acegisecurity.BadCredentialsException: Empty password
	at hudson.plugins.active_directory.ActiveDirectoryUnixAuthenticationProvider.retrieveUser(ActiveDirectoryUnixAuthenticationProvider.java:254)
	at hudson.plugins.active_directory.ActiveDirectoryUnixAuthenticationProvider.retrieveUser(ActiveDirectoryUnixAuthenticationProvider.java:219)
	at hudson.plugins.active_directory.ActiveDirectoryUnixAuthenticationProvider.retrieveUser(ActiveDirectoryUnixAuthenticationProvider.java:163)
	at org.acegisecurity.providers.dao.AbstractUserDetailsAuthenticationProvider.authenticate(AbstractUserDetailsAuthenticationProvider.java:122)
	at org.acegisecurity.providers.ProviderManager.doAuthentication(ProviderManager.java:200)
	at org.acegisecurity.AbstractAuthenticationManager.authenticate(AbstractAuthenticationManager.java:47)
	at org.acegisecurity.ui.webapp.AuthenticationProcessingFilter.attemptAuthentication(AuthenticationProcessingFilter.java:74)
	at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:252)
	at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
	at jenkins.security.BasicHeaderProcessor.doFilter(BasicHeaderProcessor.java:93)
	at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
	at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
	at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:67)
	at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
	at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
	at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:168)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
	at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
	at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
	at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1474)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:499)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:533)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:428)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
	at org.eclipse.jetty.server.Server.handle(Server.java:370)
	at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:489)
	at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:960)
	at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1021)
	at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:865)
	at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240)
	at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:668)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
	at winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)

Restarted Jenkins and got the same error: "1) Tried proxying hudson.plugins.emailext.ExtendedEmailPublisherDescriptor to support a circular dependency..." but did not get the second error: "WARNING hudson.plugins.active_directory.ActiveDirectoryUnixAuthenticationProvider retrieveUser
Credential exception trying to authenticate against uktm.eu.nec.com domain".

Yeah, the second error is not related. What version of Jenkins? What version of Mailer?

Jenkins 1.607, Mailer 1.15.

Upgraded to Jenkins 1.613 and the error is still there.

As a workaround, you can edit the hudson.plugins.emailext.ExtendedEmailPublisher.xml (I think that's the name) in JENKINS_HOME and set overrideGlobalSettings to true and restart Jenkins. You will need to reconfigure your mail server information in the Email-ext global config area.

Rolled back email-ext plugin to 2.40.1. Error is still there.

If you are willing, would you try this version of the plugin? You'd have to install via the advanced tab in the plugin manager.

Code changed in jenkins
User: Alex Earl
Path:
src/main/java/hudson/plugins/emailext/ExtendedEmailPublisher.java
src/main/java/hudson/plugins/emailext/ExtendedEmailPublisherDescriptor.java
http://jenkins-ci.org/commit/email-ext-plugin/970c7e18039b2c1c1f8af7e68c1ea48834a90524
Log:
Fix JENKINS-28402

Removed Mailer stuff from readResolve.

I will try to try the attached plugin, but can't do so yet.

With your attached plugin the error does not occur .

Somehow I missed your comment. I'll get a new version out asap then.

Removed Mailer accesses from readResolve. Should not have been there.

Reproduced in jenkins 2.55. 

18-Apr-2017 21:29:51.635 WARNING [Initializing plugin copyartifact] hudson.ExtensionFinder$GuiceFinder$FaultTolerantScope$1.error Failed to instantiate Key[type=hudson.plugins.emailext.ExtendedEmailPublisherDescriptor, annotation=[none]]; skipping this component
com.google.inject.ProvisionException: Unable to provision, see the following errors:

1) Tried proxying hudson.plugins.emailext.ExtendedEmailPublisherDescriptor to support a circular dependency, but it is not an interface.

1 error
at com.google.inject.internal.ProviderToInternalFactoryAdapter.get(ProviderToInternalFactoryAdapter.java:52)
at com.google.inject.internal.SingletonScope$1.get(SingletonScope.java:145)
at hudson.ExtensionFinder$GuiceFinder$FaultTolerantScope$1.get(ExtensionFinder.java:424)
at com.google.inject.internal.InternalFactoryToProviderAdapter.get(InternalFactoryToProviderAdapter.java:41)
at com.google.inject.internal.InjectorImpl$2$1.call(InjectorImpl.java:1016)
at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1103)
at com.google.inject.internal.InjectorImpl$2.get(InjectorImpl.java:1012)
at hudson.ExtensionFinder$GuiceFinder._find(ExtensionFinder.java:386)
at hudson.ExtensionFinder$GuiceFinder.find(ExtensionFinder.java:377)
at hudson.ClassicPluginStrategy.findComponents(ClassicPluginStrategy.java:468)
at hudson.ExtensionList.load(ExtensionList.java:365)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:303)
at hudson.ExtensionList.getComponents(ExtensionList.java:168)
at hudson.DescriptorExtensionList.load(DescriptorExtensionList.java:191)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:303)
at hudson.ExtensionList.iterator(ExtensionList.java:157)
at hudson.model.User.load(User.java:201)
at hudson.model.User.<init>(User.java:155)
at hudson.model.User.getOrCreate(User.java:463)
at hudson.model.User.getById(User.java:534)
at hudson.model.User.get(User.java:518)
at hudson.model.User.current(User.java:502)
at org.jenkinsci.plugins.scriptsecurity.scripts.ApprovalContext.withCurrentUser(ApprovalContext.java:73)
at hudson.plugins.emailext.ExtendedEmailPublisherDescriptor.setDefaultPostsendScript(ExtendedEmailPublisherDescriptor.java:514)
at hudson.plugins.emailext.ExtendedEmailPublisherDescriptor.<init>(ExtendedEmailPublisherDescriptor.java:183)
at hudson.plugins.emailext.ExtendedEmailPublisherDescriptor$$FastClassByGuice$$5dfa54d0.newInstance(<generated>)
at com.google.inject.internal.cglib.reflect.$FastConstructor.newInstance(FastConstructor.java:40)
at com.google.inject.internal.DefaultConstructionProxyFactory$1.newInstance(DefaultConstructionProxyFactory.java:61)
at com.google.inject.internal.ConstructorInjector.provision(ConstructorInjector.java:105)
at com.google.inject.internal.ConstructorInjector.construct(ConstructorInjector.java:85)
at com.google.inject.internal.ConstructorBindingImpl$Factory.get(ConstructorBindingImpl.java:267)
at com.google.inject.internal.ProviderToInternalFactoryAdapter$1.call(ProviderToInternalFactoryAdapter.java:46)
at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1103)
at com.google.inject.internal.ProviderToInternalFactoryAdapter.get(ProviderToInternalFactoryAdapter.java:40)
at com.google.inject.internal.SingletonScope$1.get(SingletonScope.java:145)
at hudson.ExtensionFinder$GuiceFinder$FaultTolerantScope$1.get(ExtensionFinder.java:424)
at com.google.inject.internal.InternalFactoryToProviderAdapter.get(InternalFactoryToProviderAdapter.java:41)
at com.google.inject.internal.InjectorImpl$2$1.call(InjectorImpl.java:1016)
at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1092)
at com.google.inject.internal.InjectorImpl$2.get(InjectorImpl.java:1012)
at hudson.ExtensionFinder$GuiceFinder._find(ExtensionFinder.java:386)
at hudson.ExtensionFinder$GuiceFinder.find(ExtensionFinder.java:377)
at hudson.ClassicPluginStrategy.findComponents(ClassicPluginStrategy.java:468)
at hudson.ExtensionList.load(ExtensionList.java:365)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:303)
at hudson.ExtensionList.iterator(ExtensionList.java:157)
at jenkins.model.Jenkins.getDescriptorByType(Jenkins.java:1518)
at hudson.plugins.copyartifact.BuildSelectorParameter.initAliases(BuildSelectorParameter.java:156)
at hudson.plugins.copyartifact.CopyArtifactPlugin.postInitialize(CopyArtifactPlugin.java:35)
at hudson.PluginManager$2$1$2.run(PluginManager.java:542)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:282)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:1063)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:210)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

Please explain why I should create a duplicate? Reopened.

Issue is the same as before and appeared in Jenkins 2.55

The original issue was fixed, this is a new issue.

There were no resolution about fix version. Reopened.

No fix version.

Not going to look at this anymore. File a new issue or don't get help. 

slide_o_mix, I asked you fix version but you have just ran away.

https://wiki.jenkins-ci.org/display/JENKINS/Email-ext+plugin#Email-extplugin-2.40.3(May20,2015)

Just wanted to add that I just got the same error on Jenkins 2.46.1 and email ext plugin version 2.57.2