/// <summary>
/// Callback method invoked when the given messages have failed to be sent.
/// </summary>
/// <param name="ex">The exception that caused the failure.</param>
/// <param name="messages">The messages being sent.</param>
protected virtual void OnFailure(Exception ex, IMessage[] messages)
{
_session.OnFailure(ex, messages);
_session.FailMessages(ex, messages);
}