[Mimedefang] MD errors: 451 4.3.2 Please try again later

[Greg McCarthy]

> What changes have you made to the default mimdefang filter?
> What version of MD are you running?
> What OS are you using?

I've used the md filter example and changed the admin email address.
MD ver 2.54 running on Slackware 10.2. I've also double checked the
permissions as well - they all seem to be correct. Its probably
something small I've overlooked, but have no idea where else to look.