[WriteLog] Rejected emails

[Alan Zack]

I am sending this with MS Mail because my Outlook mail is constantly rejected for some reason

Sent from Mail for Windows 10

After a recent MS WIN 10 update something happened with my MS Outlook to where when I try to post to the reflector my email is rejected. I get the following message:
 
<writelog at contesting.com>: host mx.contesting.com[2001:470:1:313::220] said:
    550 5.7.1 Service unavailable; client [2600:3c03::f03c:91ff:fe0c:9b6]
    blocked using zen.spamhaus.org (in reply to RCPT TO command)
 
What is zen.spamhaus.org and why is it blocking me? I have been able to make posts for over 10 years and now I can’t. My provider COX, says it is not their problem.

Only happens wit writelog. Any ideas please?

Alan K7ACZ