You're missing a newline between the "To:" line and the body:

if (open (SENDMAIL, "| $sendmailpath -t"))
{
  print SENDMAIL "Subject: $subject\n";
  print SENDMAIL "From: $from\n";
  print SENDMAIL "To: $to\n";
  print SENDMAIL "\n"       ### Need a blank line between headers and 
+body!
  print SENDMAIL "This is a test e-mail.\n\n";
  close (SENDMAIL);
[download]

In addition - use strict, even though it's not the issue here.

Michael