smtp; 501 Connection rejected by policy - please delist our ip

Hello,

Our organization has been recently recieveing bounceback e-mails with the following content:

Remote-MTA: dns; cluster1.eu.messagelabs.com
Diagnostic-Code: smtp; 501 Connection rejected by policy [7.7] 5611, please
    visit www.messagelabs.com/support for more details about this error
    message.

Can you please delist our ip 178.33.80.117?

Thank you, Chris