The E (Eastern) postcode area, also known as the London E postcode area, is the part of the London post town covering much of the eastern part of Greater London, England and also Sewardstone in Essex.he E postcode area contains two non-geographic postcode districts for high-volume business users, E77 and E98. The Eastern District Office is located on Whitechapel Road and was the eastern terminus for the former London Post Office Railway, which has been mothballed since 2003.