* comment: SMTP server settings for main: host:port
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getMailSmtpServerMainHostAndPort();

    /**
     * Get the value for the key 'mail.subject.test.prefix'. <br>
     * The value is, e.g. [Test] <br>
     * comment: The prefix of subject to show test environment or not

        // Test getMailSendMock and isMailSendMock
        assertEquals("true", fessEnv.getMailSendMock());
        assertTrue(fessEnv.isMailSendMock());

        // Test getMailSmtpServerMainHostAndPort
        assertEquals("localhost:25", fessEnv.getMailSmtpServerMainHostAndPort());

        // Test getMailSubjectTestPrefix
        assertEquals("[Test]", fessEnv.getMailSubjectTestPrefix());

        // Test getMailReturnPath