code: private String getEmail(Server server) {
          Xpp3Dom configuration = (Xpp3Dom) server.getConfiguration();
          if (configuration != null) {
              Xpp3Dom emailNode = configuration.getChild("email");
              if (emailNode != null) {
                  return emailNode.getValue();
              }
          }
          return null;
      }
docs: <pre>
  <servers>
  <server>
  <id>docker-private-registry</id>
  [...]
  <configuration>
  <email>foo@bar.com</email>
  </configuration>
  </server>
  </servers>
  </pre>