Subscriptions in Operations Manager can be complex to create and configure. The key concept to consider is how to architect them to avoid challenges where it is difficult to customize them to how you want them to work. This four part blog series (http://blogs.catapultsystems.com/cfuller/archive/2009/09/08/how-to-use-customized-groups-to-simplify-the-opsmgr-console-for-server-owners-–-using-custom-groups-to-secure-views.aspx) discusses how to architect your OpsMgr environment in a way that you can create subscriptions for entities which are relevant to the various groups within an organization. As part of this process I only email notifications on critical/high priority items so the way I address this question is through adjusting the priority/severity of the particular alert to a state other than critical/high.
Summary: If you have architected your alerts in the way that we discuss in these articles, it’s simple to exclude an alert by changing either the priority or the severity of the alert.