Complex sentence: However, for efficiency reasons, the Royal Mail decided not to expand the London postal district, so Erith, along with most of Bexley Borough, adjoins the SE postcode area but continues to be serviced from Dartford, Kent, and has DA postal codes.
Split into simpler sentences: However, for efficiency reasons, the Royal Mail decided not to expand the London postal district. Erith and most of Bexley Borough adjoin the SE postcode area but continue to be serviced from Dartford, Kent, and have DA postal codes.