The Department of Justice has been criticised for 'ad hoc' emails about garda whistleblowers.

A new review has found there is no clear system for the filing and storage of emails - however, the problems are not thought to be deliberate.

The controversy over the force's treatment of whistleblowers led to the resignation of Frances Fitzgerald as Tánaiste.

A review was ordered after it emerged not all the emails about an alleged legal strategy against Maurice McCabe at the O'Higgins Commission were provided to Judge Charleton's inquiry.

That review says that the email accounts of senior officials in the policing division and Secretary-General's office of the Department of Justice were not searched as part of the initial request from the tribunal.

Senior Counsel Michael Collins said no meaningful explanation had been given for the omission, except that it apparently did not occur to officials that those accounts may provide information of interest.

The report was also critical of how the searches were carried out, saying they were done in an ad hoc manner and there was little communication at senior level in the department about interactions with the tribunal.

The report does note there was no evidence of deliberate concealment or withholding of information, more that certain areas were omitted.

It noted a further trawl of around 30 million emails resulted in less than 80 of relevance being identified, which gives them confidence that all documents of relevance are now with the tribunal.