use POSIX ":sys_wait_h";
my $mpid = open my $mh, "| /usr/sbin/sendmail"
  or die "$!";
print $mh << "EOF";
To: joe@here.com
From: smith@here.com
Subject: data subject
message body here
EOF
close $mh
  or die "$!";
waitpid $mpid, 0;