It appears here you are opening /usr/ucb/mail and not sendmail. Otherwise, this appears it would work. In the prior line, you would need :

# old
open(MAIL,"|$mailprog -t -f  || die"" couldn't open mailprog $!")

# new
open(MAIL,"| $mailprog -t -f") || die "couldn't open mailprog $!";
[download]

hope that helps
update: this is , assuming, $mailprog is /usr/lib/sendmail

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Thus spake the Master Programmer:
"When you have learned to snatch the error code from the trap frame, it will be time for you to leave."
-- The Tao of Programming