* 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