Submit Feedback
Legacy Knowledge Base
Published Sep. 10, 2025

java.lang.ClassCastException: class javax.mail.Session cannot be cast to class javax.mail.Session error when configuring email delivery using JNDI

Written By

Jorge Diaz

How To articles are not official guidelines or officially supported documentation. They are community-contributed content and may not always reflect the latest updates to Liferay DXP. We welcome your feedback to improve How To articles!

While we make every effort to ensure this Knowledge Base is accurate, it may not always reflect the most recent updates or official guidelines.We appreciate your understanding and encourage you to reach out with any feedback or concerns.

Legacy Article

You are viewing an article from our legacy "FastTrack" publication program, made available for informational purposes. Articles in this program were published without a requirement for independent editing or verification and are provided"as is" without guarantee.

Before using any information from this article, independently verify its suitability for your situation and project.

Issue

We have configured email delivery using the application server JNDI mail resource, adding the following property to the portal-ext.properties file

mail.session.jndi.name=mail/Session 

We followed this Liferay documentation to configure it:

When we try to send an email we are getting the following exception:

2023-03-14 16:03:14.394 ERROR [liferay/mail-2][InfrastructureUtil:90] Unable to lookup mail/Session
java.lang.ClassCastException: class javax.mail.Session cannot be cast to class javax.mail.Session (javax.mail.Session is in unnamed module of loader 'javax.mail.api@1.6.5.redhat-00001' @35cb51f9; javax.mail.Session is in unnamed module of loader com.liferay.shielded.container.internal.ShieldedContainerClassLoader @345def0f)
    at com.liferay.portal.kernel.util.InfrastructureUtil._createMailSession(InfrastructureUtil.java:87) [portal-kernel.jar:?]
    at com.liferay.portal.kernel.util.InfrastructureUtil.getMailSession(InfrastructureUtil.java:51) [portal-kernel.jar:?]
    at com.liferay.mail.service.impl.MailServiceImpl.getSession(MailServiceImpl.java:193) [portal-impl.jar:?]
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?]
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
    at java.lang.reflect.Method.invoke(Method.java:566) ~[?:?]
    at com.liferay.portal.spring.aop.AopMethodInvocationImpl.proceed(AopMethodInvocationImpl.java:50) [portal-impl.jar:?]
    at com.liferay.portal.spring.transaction.TransactionInterceptor.invoke(TransactionInterceptor.java:69) [portal-impl.jar:?]
    at com.liferay.portal.spring.aop.AopMethodInvocationImpl.proceed(AopMethodInvocationImpl.java:57) [portal-impl.jar:?]
    at com.liferay.change.tracking.internal.aop.CTTransactionAdvice.invoke(CTTransactionAdvice.java:79) [bundleFile:?]
    at com.liferay.portal.spring.aop.AopMethodInvocationImpl.proceed(AopMethodInvocationImpl.java:57) [portal-impl.jar:?]
    at com.liferay.portal.spring.aop.AopInvocationHandler.invoke(AopInvocationHandler.java:49) [portal-impl.jar:?]
    at com.sun.proxy.$Proxy122.getSession(Unknown Source) [?:?]
    at com.liferay.mail.kernel.service.MailServiceUtil.getSession(MailServiceUtil.java:81) [portal-kernel.jar:?]
    at com.liferay.petra.mail.MailEngine.getSession(MailEngine.java:83) [com.liferay.petra.mail.jar:?]
    at com.liferay.petra.mail.MailEngine.send(MailEngine.java:186) [com.liferay.petra.mail.jar:?]
    at com.liferay.petra.mail.MailEngine.send(MailEngine.java:336) [com.liferay.petra.mail.jar:?]
    at com.liferay.mail.messaging.MailMessageListener.doMailMessage(MailMessageListener.java:100) [portal-impl.jar:?]
    at com.liferay.mail.messaging.MailMessageListener.doReceive(MailMessageListener.java:115) [portal-impl.jar:?]
    at com.liferay.portal.kernel.messaging.BaseMessageListener.doReceive(BaseMessageListener.java:48) [portal-kernel.jar:?]
    at com.liferay.portal.kernel.messaging.BaseMessageListener.receive(BaseMessageListener.java:34) [portal-kernel.jar:?]
    at com.liferay.portal.kernel.messaging.InvokerMessageListener.receive(InvokerMessageListener.java:74) [portal-kernel.jar:?]
    at com.liferay.portal.messaging.internal.ParallelDestination$1.run(ParallelDestination.java:56) [bundleFile:?]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
    at java.lang.Thread.run(Thread.java:834) [?:?]

Environment

  • Liferay DXP 7.4 installation using JNDI email configuration

Resolution

The root cause of this issue is javax.mail.Session class is being loaded by two different classloaders from two java libraries.

  • The first class is loaded from the mail.jar library from the application server. (loader 'javax.mail.api@1.6.5.redhat-00001')
  • The second class is loaded from the mail.jar library from the Liferay application. (loader com.liferay.shielded.container.internal.ShieldedContainerClassLoader @345def0f)).

According to the tomcat JDNI installation documentation here: https://tomcat.apache.org/tomcat-9.0-doc/jndi-resources-howto.html#JavaMail_Sessions
 
In the "4. Install the JavaMail libraries" sections, it is said:

Unpackage the distribution and place mail.jar into $CATALINA_HOME/lib so that it is available to Tomcat during the initialization of the mail Session Resource. Note: placing this jar in both $CATALINA_HOME/lib and a web application's lib folder will cause an error, so ensure you have it in the $CATALINA_HOME/lib location only.

(Although this documentation is for Tomcat, the problem with JBoss would be equivalent.)

So in order to avoid the error, the solution would be to remove the mail.jar library from the Liferay web application, so the javax.mail.Session class should always be resolved using the classloader that is at the application server level.

To remove this mail.jar library from the application server:

  1. Shutdown the application server
  2. Create a backup of [LIFERAY_HOME]/tomcat-9.x.x/webapps/ROOT/WEB-INF/shielded-container-lib/mail.jar just in in case it is necessary to restore it
  3. Delete the mail.jar from the shielded-container-lib folder
  4. Start the application server

Additional Information

 

 

 

Did this article resolve your issue ?
Legacy Knowledge Base
Did this article resolve your issue ?