Maybe a possibility??
Marriage:
HARTE Emma Elizabeth Reading 2c 607 <<<<<<<<<<<<<<
Maycock Edwin Richard Reading 2c 607
PAICE Annie Ethel Reading 2c 607
PAIGE Annie Ethel Reading 2c 607
Smith Edmund Reading 2c 607<<<<<<<<<<<<<<<<<<<<
Possibly Emma Elizabeth's surname mistakenly recorded as Harte instead of Start.
Here with her parents in 1871:
RG10/2031/176
Uplyme, Devonshire
George Start Head 40 Musbury, Devonshire
Jemima Start Wife 37 Uplyme, Devonshire
Emma Start Daughter 12 Uplyme, Devonshire<<<<<<<<<<
Emily Start Daughter 10 Uplyme, Devonshire
Elizabeth Start Daughter 8 Uplyme, Devonshire
Ann Start Daughter 6 Uplyme, Devonshire
George Start Son 4 Uplyme, Devonshire
Alfred Start Son 0 Uplyme, Devonshire
Her parents marriage:
Marriages Mar qtr 1858
George Start & Jemima Start Axminster 5b 23
Emma Elizabeth's birth:
START, EMMA ELIZABETH mothers maiden name SANSOM
GRO Reference: 1858 D Quarter in AXMINSTER Volume 05B Page 1
Smith Family in the 1891 census:
RG12/992/81 p 10
Wolseley Street Reading
Edmund Smith Head 32 b Reading, Berkshire, Bricklayer's labourer
Emma Smith Wife 32 Lyme Regis, Dorsetshire
Wm Hy Smith Son 9 Reading, Berkshire *******************
Emily L Smith Daughter 5 Reading, Berkshire
Edmund V SmithSon 3 Reading, Berkshire
Geo Smith Son 1 Reading, Berkshire
Bessie Smith Sister 26 Lyme Regis, Dorsetshire
*******************Note: William Henry born before the marriage
Birth reg:
STARTE, WILLIAM HENRY - (no maiden name entered)
1882 Jun Quarter READING Volume 02C Page 363
SMITH, EMILY LOUISE mothers maiden name START
1885 Dec Quarter READING Volume 02C Page 349
SMITH, EDMUND VICTOR mothers maiden name START
1887 Sep Quarter READING Volume 02C Page 353
This looks like Emma in 1881:
Reading St Mary, Berkshire, England
Coley Hill<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
RG11/1301/74 p 12
Emma Start 24 b Devon Domestic servant
So could the W Start in the list of Newbury Postmen that you mention be the illegitimate sone of Emma Elizabeth Smith (nee Start).
Family search have this for William Henry Starte which records him as a postman(3rd one down):
https://tinyurl.com/y7bm46l8 (note where born)
Death for him:
Deaths Dec 1939
Starte William H 57 Newbury 2c 671
Kind Regards
Chris