[Mimedefang] Milter: data, reject=451 4.7.1 Please try again later

[Lu]

OS: Solaris 5.7
sendmail: 8.12.3
mimedefang: 2.11

All legitimate e-mails are not going through - yet no bounce either.
Log entries in /var/log/syslog shows:

Milter: data, reject=451 4.7.1 Please try again later

I have heard of a milter patch but that was for sendmail 8.12.2.  I
don't think a patch is needed for this version of sendmail

Please let me know what could be the problem here.

Thanks.

Lu