Net::SMTP not sending CC correctly

I'm having an issue wherein I can't get Perl's Net::SMTP module to send to multiple addresses.
Whichever address I put in the first "To:" entry is sent correctly, but I can't get CC to work.
I've also tried putting multiple addresses in the "To:" entry and experience the same results.

I can see the correct information in the email I receive via the first "To:" entry (ie. the email shows the CC entry properly) but the email is not sent to the second address regardless of where I place it.

Here is a snip of the Perl script where Net::SMTP is implemented:
--------------------------------------------------
sub send_mail {
  my ($smtp_to, $smtp_subject, $smtp_body, $smtp_cc1) = @_;
  my $smtp_host = 'x.x.x.x';   # masked ip (confidential)
  my $smtp_from = hostname."\@domain.com";   # masked domain (confidential)
  my $smtp_message;
  eval { $smtp_message = Net::SMTP->new($smtp_host) };
    if ($@) { warn "Unable to open the SMTP connection: $! <Net::SMTP->new($smtp_host)>" };
  eval { $smtp_message->mail($smtp_from) };
    if ($@) { warn "Unable to open the SMTP connection: $!<$smtp_from>" };
  $smtp_message->to($smtp_to);
  $smtp_message->data();
  $smtp_message->datasend("To: $smtp_to\n");
  $smtp_message->datasend("cc: $smtp_cc1\n") if (defined $smtp_cc1);
  $smtp_message->datasend("Subject: $smtp_subject\n");
  $smtp_message->datasend("\n");
  foreach my $smtp_body_line  (@$smtp_body) {
    chomp($smtp_body_line);
    $smtp_message->datasend("$smtp_body_line\n");
  }
  $smtp_message->dataend()
    or warn "Error in SMTP-dataend command: $!";
  $smtp_message->quit
    or warn "Error in SMTP-quit command: $!";
  warn "SMTP Message sent to $smtp_to with subject: $smtp_subject" if $trace_level > 1;
}


Here is the line where the email is sent:
--------------------------------------------------
send_mail('address1@domain.com', $lv_email_subject, \@la_email_body,'address2@domain.com')
  or warn "ATTENTION: send_mail subroutine failed: $!";

The mail server log only shows the first address as being received (no CC):
--------------------------------------------------
Aug 22 12:27:04 mailhost sendmail[10140]: [ID 801593 mail.info] l7MGR3Tt010139: to='address1@domain.com', delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=30845, relay=inbound.netidentit...rehostedemail.com. [ip address], dsn=2.0.0, stat=Sent (<46CC3A620005A3E7> Mail accepted)

However the header seems to be setup correctly as I can see the CC in the email I receive via the TO address:
--------------------------------------------------
From: hostname@domain.com [mailto:hostname@domain.com]
Sent: Wednesday, August 22, 2007 12:10 PM
To: address1@domain.com
Cc: address2@domain.com


I can flip the address1 and address2 back and forth and always receive only whichever is first in the TO/CC.
I've also tried using multiple "To:" entries in the send_mail subroutine (ie. 2 lines with "To:" in stead of "To:" and "cc:") and I experience the same issue - only the first address in the list is received (and I can see both entries in the header from the one email I receive)

I've tested CC using "mailx" on a unix system and it worked correctly, so there is no problem with the mail server itself.
FYI - The above perl scripts are running on a windows machine.