The Mail Threat Protection component applies various groups of settings to protect mail. The settings groups are called email security levels. There are three email security levels: High, Recommended, and Low. The Recommended file security level is considered the optimal setting, and is recommended by Kaspersky. You can select one of the pre-installed email security levels or configure a custom email security level. If you have changed the email security level settings, you can always revert to the recommended email security level settings.
To change the email security level:
After you configure a custom email security level, the name of the security level in the Security level section changes to Custom.