How to create mock email service in Java?

I am writing a small testing library with different mock services such as HTTP, SFTP, Buckets, Email.

I have a mind block when it comes to Email Mock service. I find a Apace James docs and an article but I don't see how I can adapt it to my interface and it is confusing to work with SMTP Servers.

interface TestServer {

    void start();

    void stop();

}

The idea is to create an implementation, so the whole setup will be in the constructor and I need to start and stop Mock only in set up and tear down phases.

How can I do it with the Apache James service?

I use Java 11, Spring Boot, and JUnit 5.