[exim] Too many syntax or protocol errors

I'm getting

2007-10-19 13:04:46 SMTP call from (localhost.localdomain) [127.0.0.1]
dropped: too many syntax or protocol errors (last command was "")

When running this script:

use strict;
use Net::SMTP;

my $mailserver = "127.0.0.1";
my $mailfromname = "Training Diary";
my $mailfrom = "127.0.0.1";
sub mail {
        my($mailto, $subject, $text) = @_;

        my $smtp = Net::SMTP->new($mailserver);
        $smtp->mail($mailfrom);
        $smtp->to($mailto);
        $smtp->data();
        $smtp->datasend("From: $mailfromname <$mailfrom>\n");
        $smtp->datasend("To: $mailto\n");
        $smtp->datasend("Subject: $subject\n");
        $smtp->datasend('Content-Type: text/html; charset=ISO-8859-1', "\n");
        $smtp->datasend('Content-Transfer-Encoding: 7bit', "\n\n");
        $smtp->datasend("$text\n");
        $smtp->dataend();
        $smtp->quit;

        return "1";
}

1;
I've set these additional settings in exim.conf:
smtp_max_synprot_errors = 50
smtp_enforce_sync = false
smtp_max_unknown_commands = 100
sender_unqualified_hosts = localhost

Any ideas on how to fix this?