Red-faced Royal Borough bosses are making their entire 1,500-strong workforce sit through data protection training after sensitive information sent from another council was lost.
They have also apologised to Southampton City Council after a package it sent containing social care information disappeared in their system.
An ICO spokesman said it had looked at the issue and no further action will be taken.
The decision was made after it looked at the existing measures the borough had in place and the action taken after the problem was flagged.
The ICO will also keep a record of the problem and may revisit it again if similar issues surface.
A statement from the Royal Borough said immediate action was taken to identify how the loss occurred and to introduce 'stringent' checking systems for the receipt and distribution of special delivery packages.
Managing director Mike McGaughrin said: "We take data protection and information security matters very seriously and acted immediately this very regrettable incident took place.
"It prompted a review of our post room procedures so that urgent improvements could be made.
"We are also undergoing a programme of training and refresher training for every employee so there is universal awareness about the importance of data security."
All council staff will receive a two-hour training session provided by its in-house data protection and security staff.
Southampton City Council declined to comment.
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