Hab was vergessen. Du solltest natürlich auch stets use strict verwenden, also :
#!/usr/bin/perl -w
use strict;
print "Content-type: text/html\n\n";
my $mailprog = '/usr/sbin/sendmail -i -t';
open(MAIL,"|$mailprog") || die "$!";
print MAIL "To: deinemail@test.com\n";
print MAIL "From: foo@bar.com\n";
print MAIL "Subject: Mein tolles Subject\n\n";
print MAIL "Das\nist\nein\nTest\n\n";
close (MAIL);
print "Dieses Script sollte eine Mail senden...";
$xNeTworKx.