A gang of fraudsters targeted five affluent apartment blocks in Norwich and cleaned out people's bank accounts.
They preyed on around 200 victims across the country, using false identities to gain tenancies in flats and access mail boxes in communal areas.
Victims' bank details were then stolen, with bank insiders helping the gang to order replacement cards which were then intercepted to drain accounts of cash.
Frauds of more than £290,000 were linked to the group, however the real figure is believed to be much higher.
In Norwich, the gang of 10 people targeted four blocks of flats in King Street - Albion Mill, New Ferry Yard, New Half Moon Yard and The Malt House - and a fifth block, Allison Bank in Geoffrey Watling Way.
They targeted 21 separate apartment blocks across the country, with the other addresses in Doncaster, Liverpool, London, Nottingham, Sheffield and Tunbridge Wells.
Ten people were this week sentenced at Ipswich Crown Court for their involvement in the fraud.
The convictions follow a lengthy investigation by the Suffolk and Norfolk Cyber and Serious Crime Department.
Detective Superintendent Steve Mattin, department head, said: 'A number of constabularies were involved in bringing this team to justice on what was an extensive and comprehensively planned fraud, that targeted innocent members of the public.
'A lot of work was done by officers in Suffolk and Norfolk, Kent and Merseyside to secure sufficient evidence to prosecute these individuals and the sentences reflect the nature of the fraud and send a strong message that those found to be committing this type of offence will be traced and put before the courts.
'We will pursue those who take part in organised crime and take action against them.'
Access to the blocks was obtained by members of the group who obtained tenancies using stolen identities and by producing false employment references.
At least two bogus companies were set up to provide these references and landline numbers were also purchased via the internet to give these companies the appearance of legitimacy.
DC Duncan Wallace, officer in the case, said; 'The tenants' post was then targeted with members of the crime group accessing individual mailboxes, situated in communal areas on the ground floor, which they were able to open by use of a master key.
'Victims' bank and credit card statements were stolen and bank staff working for the crime group then provided confidential information about the victims bank accounts which enabled replacement bank cards and PINS to be ordered.
'These replacement cards and PINs were intercepted in the victims' mailbox and then used to withdraw cash, purchase foreign currency or purchase high value goods.
'The victim was totally unaware of this activity on their bank account and it is only when they were unable to access funds that the fraud was discovered.'
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