Postboxes were locked in Long Eaton this week just weeks after a set of keys went missing in Ilkeston forcing the slots there to be sealed shut.
The locked boxes, in Station Road, Bonsall Street and Conway Road in the town, were first reported locked on Friday and were still blocked off on Monday.
Royal Mail spokesperson Heulyn Gwyn Davies said: “I am afraid that we have had to seal a number of postboxes in the Long Eaton area for security reasons due to keys going missing.
“All mail has been removed from the affected boxes and has been processed through the postal system. New locks will be installed in these boxes and they should all be back in service by next week.
“We apologise to customers for any inconvenience caused while the boxes were out of action. No mail was delayed and thankfully this is a rare occurrence.”