From OpenNMS

Rationale

If notifications are sent around, it's advisable to look into the WebUI to understand their scope. To do that, you need to connect to OpenNMS, search for the node and have a look (well, you probably can find the notice as well).

Implementation

To ease that process, I added this to notifications.xml:

        <text-message xmlns="">All services are down on node %nodelabel%.
        New Outage records have been created and service level availability calculations will
        be impacted until this outage is resolved.
        The status for this node: https://my.opennms.com/opennms/element/node.jsp?node=%nodeid%
        </text-message>

The message sent out then is

       All services are down on node %nodelabel%.
       New Outage records have been created and service level availability calculations will
       be impacted until this outage is resolved.
       The status for this node: https://my.opennms.com/opennms/element/node.jsp?node=123

Which allows the receiver to just click on the mail and go.