Sendmail isn't working like it's supposed to...

Okay, here's the deal.  I've got a site on Hypermart and they say "The mail program is located at /var/qmail/bin/qmail-inject. You would use it the same way you use 'SendMail', by piping things into it."  So I throw this code into a perl script towards the top where it'll be sure to be run.  I access the script, but don't get any email.  What's my problem?

open(MAIL, "|/var/qmail/bin/qmail-inject -t") or print "ERROR, DUDE!";
print MAIL "To: assignat@yahoo.com\n";
print MAIL "From: assignat@yahoo.com\n";
print MAIL "Subject: This is lovely, eh?\n";
print MAIL "What do you think?  Did this work?  Huh?\n\n-Brian\n";
close(MAIL);

-Brian