java.lang.NoClassDefFoundError: com/sun/mail/util/MailLogger for JUnit test case for Java mail

The javax.mail-api artifact is only good for compiling against.

You actually need to run code, so you need a complete implementation of JavaMail API. Use this:

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

NOTE: The version number will probably differ. Check the latest version here.

com.sun.mail.util.MailLogger is part of JavaMail API. It is already included in EE environment (that's why you can use it on your live server), but it is not included in SE environment.

Oracle docs:

The JavaMail API is available as an optional package for use with Java SE platform and is also included in the Java EE platform.

99% that you run your tests in SE environment which means what you have to bother about adding it manually to your classpath when running tests.

If you're using maven add the following dependency (you might want to change version):

<dependency>
    <groupId>com.sun.mail</groupId>
    <artifactId>javax.mail</artifactId>
    <version>1.6.0</version>
</dependency>

I use the following maven dependencies to get java mail working. The first one includes the javax.mail API (with no implementation) and the second one is the SUN implementation of the javax.mail API.

<dependency>
    <groupId>javax.mail</groupId>
    <artifactId>javax.mail-api</artifactId>
    <version>1.5.5</version>
</dependency>
<dependency>
    <groupId>com.sun.mail</groupId>
    <artifactId>javax.mail</artifactId>
    <version>1.5.5</version>
</dependency>