ITP/Server requests are handled under MQSeries syncpoint control. As a result, requests are handled as an atomic transaction for as far as MQSeries communication is concerned. Furthermore, if the interface cannot deliver a request to ITP/Server, it will be backed-out so that it can be processed later (in that case, it is certain that it did not yet have any side-effects).
In most cases, if a job does get delivered to ITP/Server, and it fails, it will not be backed out, but a failure will be reported. This is better than backing out, as this usually indicates a serious problem that will not get solved by just resubmitting the job. In addition, a failed job may have had some side-effect that may need to be taken into account.
There is only one case that job may get backed-out after being delivered to ITP/Server. This will only happen in case the MQSeries interface ends abnormally. This however, is a very unlikely event that will not go unnoticed.