você pode tentar este comando awk?
$ xxxcommand | awk 'NR==1{printf("%-10s%-10s%-10s%-10s\n",$1,$2,$3,"calculation")}NR>1{printf("%-10s%-10s%-10s%-10s\n",$1,$2,$3,$2/$3)}' | mail_command
Name Files(n) Space calculation
Adam 12345 12345 1
Becky 45689 8987 5.0839
Maryanne 5598 7895 0.709056