Residents in some areas of Hainault and Barkingside have been unable to post letters for more than a week after Royal Mail lost the key to a number of nearby postboxes.
It is believed that a large number of freestanding postboxes in nearby streets have been affected, but postboxes outside post offices are still in use.
Mail can also be dropped off at any open post office.
A Royal Mail spokeswoman said: “We can confirm that unfortunately a small number of postboxes in Barkingside and Hainault are currently out of service after the keys were misplaced.
“Royal Mail would like to apologise to customers for any inconvenience this may have caused.
“New keys are on order and we hope to reopen the boxes soon.
“In the meantime, customers can use other boxes in the area or drop off mail at any Post Office branch.”
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