# IMS Events or Triggers

Substation ES supports both the receiving and publishing of IMS Asynchronous and Synchronous events or messages. Programs such as MPPs or BMPs can publish events by Substation directly onto ESB.

Substation ES does not require the OTMA exits to be installed in order to deliver outbound events. To enable outbound events, you must update the IMS member `DFSTDYxx` and define IMS descriptors. Product installation sample member `DFSYDT0` in `USERHLQ.PROC` contains the recommended default Substation ES definitions.

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