Privacy concerns have been raised after the personal details of thousands of former Australian Defence Force personnel were wrongly sent out in an email.

The Defence Community Organisation, which helps families adjust to military life, emailed a database of nearly 2,500 former Defence staff to around 400 other ex-service personnel.

The information included names, identification numbers, personal email addresses, type of service and their reason for leaving.

An initial inquiry has found computer security first blocked the email, but a staffer was told to try sending it again.

The ADF says it is treating the matter with the utmost seriousness.

A Defence spokesperson says an external consultant is undertaking a formal investigation.

"Staff members involved in the incident have been counselled and staff have been directed to undertake privacy training," the spokesperson said.

Defence Force Welfare Association national president, retired Colonel David Jamison, says it is a serious breach of privacy.

"Somebody has ignored the warning that was given and then released the email in a way that it's designed not to happen, but it just did," he said.

"So it's a human error that is difficult to sort of stop sometimes."

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