When adding mail config via jboss-cli with an invalid hostname this leads to an NPE:
29.08. 22:33:10,293 INFO org.jboss.as.mail.extension#transition WFLYMAIL0001: Bound mail session [java:/Mail]
29.08. 22:33:10,367 ERROR org.jboss.msc.service.fail#startFailed MSC000001: Failed to start service jboss.mail-session.java:/Mail: org.jboss.msc.service.StartException in service jboss.mail-session.java:/Mail: Failed to start service
at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1904) [jboss-msc-1.2.2.Final.jar:1.2.2.Final]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [rt.jar:1.7.0_67]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [rt.jar:1.7.0_67]
at java.lang.Thread.run(Thread.java:745) [rt.jar:1.7.0_67]
Caused by: java.lang.NullPointerException
at org.jboss.as.mail.extension.SessionProviderFactory$ManagedSession.setServerProps(SessionProviderFactory.java:129)
at org.jboss.as.mail.extension.SessionProviderFactory$ManagedSession.configure(SessionProviderFactory.java:87)
at org.jboss.as.mail.extension.SessionProviderFactory$ManagedSession.<init>(SessionProviderFactory.java:72)
at org.jboss.as.mail.extension.SessionProviderFactory$ManagedSession.<init>(SessionProviderFactory.java:64)
at org.jboss.as.mail.extension.SessionProviderFactory.create(SessionProviderFactory.java:45)
at org.jboss.as.mail.extension.MailSessionService.start(MailSessionService.java:60)
at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1948) [jboss-msc-1.2.2.Final.jar:1.2.2.Final]
at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1881) [jboss-msc-1.2.2.Final.jar:1.2.2.Final]
... 3 more

29.08. 22:33:10,389 ERROR org.jboss.as.controller.management-operation#executeStep WFLYCTL0013: Operation ("add") failed - address: ([
("subsystem" => "mail"),
("mail-session" => "java:/Mail")
]) - failure description: {"WFLYCTL0080: Failed services" => {"jboss.mail-session.java:/Mail" => "org.jboss.msc.service.StartException in service jboss.mail-session.java:/Mail: Failed to start service
Caused by: java.lang.NullPointerException"}}
29.08. 22:33:10,416 INFO org.jboss.as.controller#logContainerStateChangesAndReset WFLYCTL0183: Service status report
WFLYCTL0186: Services which failed to start: service jboss.mail-session.java:/Mail