An Garda Síochána has confirmed that Garda Commissioner Nóirín O'Sullivan used a commercial email service to send official garda correspondence, but said that her email systems are secure and there is no evidence they have ever been compromised.

In a statement this afternoon, An Garda Síochána said: "Due to restrictions with the Garda email system such as e-mail size and storage, the Commissioner occasionally used a Gmail address to ensure that Garda business has been discharged effectively."

It added: "At all times, there has been due regard to the sensitivity of any information being transmitted in this way."

A senior garda officer earlier told RTÉ News he communicated with Garda Commissioner Nóirín O'Sullivan on official business through a commercial email address when she was deputy commissioner.

The officer said on at least one occasion he sent Commissioner O'Sullivan an official report.

He also said that on another occasion he received an email from the commissioner from that email address on a separate garda matter.

Gmail accounts are set up by the garda's IT section on official garda phones and iPads, but RTÉ News understands that communicating garda business through this system could be contrary to the internal and electronic mail policy in An Garda Síochána.

In this afternoon's statement, An Garda Síochána said the force's policy on email "dates from 2012 and does not take into account advances in technology since then such as the need for mobile devices to be associated with a commercial email address in order for them to be secured and configured.

"The 2012 policy has recently been reviewed and a new policy is being finalised."

The Sunday Times first reported that Ms O'Sullivan had been using a private email account to send and receive official correspondence.

RTÉ News has seen a print out of an email from 2013 when Ms O'Sullivan was deputy commissioner in charge of operations with her name and rank printed at the bottom.

The deputy commissioner of operations is in charge of all crime and security matters as well as State security and intelligence.

The document did not appear to relate to any of these sensitive matters but to another area of garda policy.

The Policing Authority has said while it will be in contact with An Garda Síochána on the issue.

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