Found JENKINS-28402 with the same error, but different version of the plugin (and it's closed)

With a suggestion from the mailing list (thanks Victor!) , after downgrading the email-ext plugin from 2.57.2 to 2.40.3 we don't see the circular dependency error anymore (we get template error, but that's because the version of email-ext is no longer compatible)

WARNING: 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)jjjjjjj

        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:472)

        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:472)

        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:1519)

        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:543)

        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:1064)

        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)