Since Plesk Automation 11.5 MU#18 Greylisting and DomainKeys protection are implemented.
How to enable?
Both services by default are disabled and must be specifically enabled on per-service node basis in Provider's panel -> Service Nodes -> Mail node -> Mail Settings (or Spamfilter settings for Greylisting).
Once greylisting are enabled - it is active for all mailboxes on server. Once domainkeys are enabled - it is not active, until mail users enable it in CCP for themselves.
How to configure?
Greylisting can be configured only via command line utility.
Usage details are described in knowledge base article #6359, but commands must be run on the management node only, and additional console parameter
-service-node should be used, to manage specific service node.
DomainKeys are configured in customer control panel.