Unable to Send Email to Certain Domains

Hi Support,

Currently our domain is unable to send any emails to all domains administrered by Message Labs. We receive a bounce back email saying it was blocked due to message filtering. I have searched and was unable to find a way to get our domain unblocked. My question is how do I go about getting our domain unblocked to all domains administered by Message Labs as we arent able to get a direct contact without already being a customer.