Further or farther

Please email me for further information.  To reach the post office, walk farther down the street. Further, fartherโ€ฆ Whatโ€™s the difference? Is it just two different spellings of the same word? The answer is yesโ€”and no. Please read on for some explanation. Both โ€˜furtherโ€™ and โ€˜fartherโ€™ are irregular comparative forms of the same adjective (and …