501 Connection rejected by policy [7.7] 13009

One of our clients receive an error message like this:

host cluster3.eu.messagelabs.com [85.158.137.35]

    SMTP error from remote mail server after initial connection:

    501 Connection rejected by policy [7.7] 13412, please visit www.messagelabs.com/support for more details about this error message

I've fill a form last week to whitelist our IP address, but the problem continues.

I've checked our Ip address agains other RBLS and I don't get any block, I also tried to send a private message to Richard Brittain explaning this issue but the "forum" always returns to me that my message was block with a spam filter.

Can someone please help with this issue?

Our Ip address is 185.31.158.175

I apologize in advance for my English