Can't send email after switching ISP

I have Cox for email only (they are not a provider where I moved to.)  Up until recently mail worked fine but I just switched ISP's and now I can't send.  I get these messages:

cxr-obgw-6001a.stratus.cloudmark.com cmsmtp 136.244.54.211 blocked. Refer to Error Codes section at www.cox.com/.../email-error-codes.html for more information. AUP#CXDNS

My new ISP seems to think the fix is on Cox because they (the ISP) are using Google for DNS. 

Where do I turn to fix this?