See MIME::Lite.

sub sendemail {
    our $file;

    use Mail::Sendmail;
    use MIME::QuotedPrint;
    use MIME::Base64;

    my %mail = (smtp    => 'smtp-int',
                To    => 'foo@bar.com, foo2@bar.com',
                Cc    => '',
                From    => 'no-reply@foobar.com>',
                Subject    => 'Email subject'
            );

    my $boundary = "====" . time() . "====";
    $mail{'content-type'} = "multipart/mixed; boundary=\"$boundary\"";

    my $message = encode_qp( "Email body. Also use to be called messag
+e." );

    open (F, $file) or die "Cannot read $file: $!";
    binmode F; undef $/;
    $mail{body} = encode_base64(<F>);
    close F;

    $boundary = '--'.$boundary;
$mail{body} = <<END_OF_BODY;
$boundary
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

$message
$boundary
Content-Type: application/octet-stream; name="$file"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="$file"

$mail{body}
$boundary--
END_OF_BODY

    sendmail(%mail) or die $Mail::Sendmail::error;
}
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Thanks very much Hawk, that's great!