My solution uses Mail::Send and sendmail only:

sub sendAttachment
{
   my( $from, $to, $subject, $filename, $type, $data ) = @_;

   my $boundary = '==' . time . '==';

   # untaint stuff for mailing
   $ENV{'PATH'} = '/bin:/usr/bin';
   delete @ENV{'IFS', 'CDPATH', 'ENV', 'BASH_ENV'};

   my $msg = new Mail::Send;
   $msg->to($to);
   $msg->add('From',$from);
   $msg->subject($subject);
   $msg->add('Content-Type', qq(multipart/mixed; boundary="$boundary";
+) );

   my $fh = $msg->open;
   print $fh "--$boundary\n";
   print $fh "Content-Disposition: attachment; filename=$filename;\n";
   print $fh "Content-Type: $type; name=$filename; charset=iso-8859-1;
+\n";
   print $fh "Content-Transfer-Encoding: 8bit;\n\n";
   print $fh $data;
   print $fh "--$boundary\n";
   $fh->close;
}
[download]

sendAttachment(
    '"Me, Here" <me@here.org>',
    'user@foo.com',
    'Quarterly Report - Q1 2007',
    'report-q12007.csv',
    'text/csv',
    $data
);
[download]