In 1917, the postal districts were numbered alphabetically by their most important parish, chapelry, topographical or built environment feature.

When districts are used for purposes other than the sorting of mail, such as use as a geographic reference and on street signs, E1 and E1W continue to be commonly classed as one 'district'.

The railway ran 10.5 kilometres (6.5 mi) to the Paddington Head District Sorting Office.

The River Roding and the North Circular Road form part of the boundary in the east.

Also, the eastern part of the London Borough of Hackney, the western sections of the London Boroughs of Redbridge (E11, E12, E18) and Barking and Dagenham (E6) and a small part of the Epping Forest District (E4), are within the postcode area.