501 Connection rejected by policy [7.7]

Hi,

We have a problem to our email server, when we send some email to our client we have this error :

"501 Connection Rejected by policy [7.7]" ... please visit www.messagelabs.com/support ...

We have checked our mailserver to ensure is properly configured and not blacklisted in any known RBL and our SPF record is correct.

Please check your system and authorize our IP address : 158.255.99.67 and 188.165.78.47

Thanks in advance