[java] java.lang.NoClassDefFoundError: javax/mail/Authenticator, whats wrong?

When I had this problem, I had included the mail-api.jar in my maven pom file. That's the API specification only. The fix is to replace this:

<!-- DO NOT USE - it's just the API, not an implementation -->
<groupId>javax.mail</groupId>
<artifactId>javax.mail-api</artifactId>

with the reference implementation of that api:

<groupId>com.sun.mail</groupId>
<artifactId>javax.mail</artifactId>

I know it has sun in the package name, but that's the latest version. I learned this from https://stackoverflow.com/a/28935760/1128668