Spam simpletons

What the hell is going on with Message Labs? Mail from my Yahoo email account keeps bouncing back with the following message:

Hi. This is the qmail-send program at yahoo.com.
I'm afraid I wasn't able to deliver your message to the following
addresses. This is a permanent error; I've given up. Sorry it didn't work out.

[email address]: [ip address] failed after I sent the message.
Remote host said: 553-Message filtered. Please see the FAQs section on
spam 553-at http://www.messagelabs.com/support/ for more
553 information. (#5.7.1)

The solution to this problem? Wait a few hours or until the next day and then resend the message.

Make your mind up, Message Labs. Either it's spam or it isn't. It can't be worthy of blocking one day and then fine the next!