text: The MX management and Domain management rules in the Email processing rules menu.
  The Message delivery duration parameter in the Configuration menu. For more on this, see this section.
  The Delivery duration or Validity limit for sending messages parameter in the Validity period section. For more on this, see this section.
  The Bounce mails rules in the Email processing rules. For more on this, see this section.
  DKIM (DomainKeys Identified Mail) email authentication signing is done by the Enhanced MTA for all messages with all domains. It does not sign with Sender ID, DomainKeys, or S/MIME unless otherwise specified at the Enhanced MTA level.