Help wanted on Sendmail

[sachin <sachin@lgeil.com>]

a=-1
for file in sup.*.txt
do
b= awk '/@/ {print $1}' $file
c= awk '/@/ {print $2}' $file
a=`expr $a + 1`
cat heading $file >>$file.txt
done
b= awk '/@/ {print $1}' sup.00.txt
echo $b # Output is sachin@lgeil.com
/usr/lib/sendmail -f sachin $b <sup.00.txt 
#the above line gives the error which is

sachin... Recipient names must be specified
Saving message in /kamal/sachin/dead.letter

and if I use 
mail $b < sup.00.txt then it displays the contents of the file &
the usage 
of the mail

TIA
Sachin