| Thanks for the help. I basically copied the ee10-demo-jndi.mod and created my own mod. I installed the mod without problems, all files copied and the Datasource works without problems.  
 The MailSession still does not work. 
 Instead of returning jakarta.mail.Session still returning MailSessionReference  even though the documentation says that lookup for  java:comp/env/mail/Session  at runtime would obtains a  jakarta.mail.Session. 
 I get the following exception: 
 java.lang.ClassCastException: class org.eclipse.jetty.ee10.jndi.factories.MailSessionReference cannot be cast to class jakarta.mail.Session (org.eclipse.jetty.ee10.jndi.factories.MailSessionReference and jakarta.mail.Session are in unnamed module of loader java.net.URLClassLoader @557caf28) 
 This is what I have in my web.xml for the datasource and mailsession 
 <resource-ref>
     <res-ref-name>jdbc/DataSource</res-ref-name>
     <res-type>javax.sql.DataSource</res-type>
     <res-auth>Container</res-auth>
 </resource-ref>
 <resource-ref>
     <res-ref-name>mail/Session</res-ref-name>
     <res-type>jakarta.mail.Session</res-type>
     <res-auth>Container</res-auth>
 </resource-ref>
 
 These are my my_webapp.mod,my_webapp.properties and my_webapp.xml files 
 -- my_webapp.mod -- 
  [description]
         My Webapp (Module for Jetty)
 
 [environment]
         ee10
 
 [tags]
         webapp
 
 [depends]
         ee10-deploy
         ext
         jdbc
         ee10-plus
         ee10-jndi
 
 [files]
         webapps/my_webapp.war
         webapps/my_webapp.xml          webapps/my_webapp.ini          maven://jakarta.mail/jakarta.mail-api/2.1.5/jar|lib/ee10/jakarta.mail-api-2.1.5.jar
         maven://jakarta.activation/jakarta.activation-api/2.1.4/jar|lib/ee10/jakarta.activation-api-2.1.4.jar
         maven://org.eclipse.angus/angus-activation/2.0.3/jar|lib/ee10/angus-activation-2.0.3.jar
         maven://org.eclipse.angus/angus-mail/2.0.5/jar|lib/ee10/angus-mail-2.0.5.jar
         maven://com.mchange/c3p0/0.11.2/jar|lib/ee10/c3p0-0.11.2.jar
         maven://com.mchange/mchange-commons-java/0.3.2/jar|lib/ee10/mchange-commons-java-0.3.2.jar
 
 [lib]
         lib/ee10/jakarta.mail-api-2.1.5.jar
         lib/ee10/jakarta.activation-api-2.1.4.jar
         lib/ee10/angus-activation-2.0.3.jar
         lib/ee10/angus-mail-2.0.5.jar
         lib/ee10/c3p0-0.11.2.jar
         lib/ee10/mchange-commons-java-0.3.2.jar
         lib/ee10/jdbcdriver.jar  
 --- my_webapp.properties 
     environment: ee10 
 --- my_webapp.xml 
 <?xml version="1.0"?> <!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "https://jetty.org/configure_10_0.dtd "> <Configure id="wac" class="org.eclipse.jetty.ee10.webapp.WebAppContext">   <Set name="contextPath">/</Set>   <Set name="war"><Property name="jetty.webapps" default="." />/my_webapp.war   </Set>   <Set name="extractWAR">true</Set>   <Set name="copyWebDir">false</Set>   <Set name="configurationDiscovered">true</Set>   <New id="db" class="org.eclipse.jetty.plus.jndi.Resource">     <Arg>       <Ref refid="wac" />     </Arg>     <Arg>jdbc/DataSource</Arg>     <Arg>         <New class="com.mchange.v2.c3p0.ComboPooledDataSource">             <Set name="DriverClass">???</Set>             <Set name="JdbcUrl">???</Set>             <Set name="User">???</Set>             <Set name="Password">???</Set>         </New>     </Arg>   </New>   <New id="mailer" class="org.eclipse.jetty.plus.jndi.Resource">     <Arg>       <Ref refid="wac" />     </Arg>     <Arg>mail/Session</Arg>     <Arg>       <New class="org.eclipse.jetty.ee10.jndi.factories.MailSessionReference">         <Set name="user">???</Set>         <Set name="password">???</Set>         <Set name="properties">           <New class="java.util.Properties">             <Put name="mail.smtp.auth">false</Put> <!-- change to true if you want to authenticate -->             <Put name="mail.smtp.host">???</Put>             <Put name="mail.from">???</Put>             <Put name="mail.debug">false</Put>           </New>         </Set>       </New>     </Arg>   </New> </Configure> |