Wenn man die Fehlermeldung bekommt

Exception in thread "main" java.lang.NoClassDefFoundError: com/sun/mail/util/MailLogger
        at javax.mail.Session.initLogger(Session.java:283)
        at javax.mail.Session.(Session.java:268)
        at javax.mail.Session.getDefaultInstance(Session.java:378)
        at javax.mail.Session.getDefaultInstance(Session.java:418)
        at eu.masterdevops.sendmail.App.main(App.java:25)
Caused by: java.lang.ClassNotFoundException: com.sun.mail.util.MailLogger
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
        … 5 more

dann fehlt vermutlich eine Abhängigkeit in der pom.xml:

<dependency>
  <groupId>com.sun.mail</groupId>
  <artifactId>javax.mail</artifactId>
  <version>1.6.2</version>
</dependency>