Event definition in the class:

public class MessageSelector : ClientJobStepBase
{
   public event MessagesSelected OnMessageSelection;
[...]
}

Call delegate:

public class MessageSelector : ClientJobStepBase
{
[...]
       List<IMessage> selectedMessages = new List<IMessage>();
[...]
       Job.Delegate(OnMessageSelection, new MessageSelectionArgs(selectedMessages));
[...]
}