Client host rejected: Connection rejected due to site policy

[Old_Professor]

I'm trying to send email to someone at University of Cagliari in Italy. His email is xxxxx@unica.it. Comcast is refusing to send the message, returning the perminant error message below.

I know that the address is good. My friend (not using Comcast) has no problem sending email to this person. I believe that Comcast has some sort of blacklist/whitelist that I can access to permit my email to go through; what is it?

To eliminate the false premise that the problem had something to do with my email client, the message rejected  below was sent using Xfinity webmail.

................. perminant error message from Comcast follows

Date: Wed, 06 May 2020 18:51:21 +0000
From: mailer-daemon@comcast.net
Subject: Permanent Error

Content-Type: text/plain; charset=UTF-8;

Content-Transfer-Encoding: 8bit

      This is an automatically generated Delivery Status Notification.     

Delivery to the following recipients failed permanently:

   * xxxxxx@unica.it

Reason: Permanent Error

Content-Type: message/delivery-status; charset=UTF-8;

Content-Transfer-Encoding: 8bit

Reporting-MTA: dns; resqmta-po-05v.sys.comcast.net [96.114.154.164]

Received-From-MTA: dns; resomta-po-20v.sys.comcast.net [96.114.154.244]

Arrival-Date: Wed, 06 May 2020 18:51:19 +0000

Final-recipient: rfc822; giacinto@unica.it

Diagnostic-Code: smtp; 550 5.7.1 <resqmta-po-05v.sys.comcast.net[96.114.154.164]>: Client host rejected: Connection rejected due to site policy

Last-attempt-Date: Wed, 06 May 2020 18:51:21 +0000

 

[ComcastCSAEmail · Accepted solution]

The domain unica.it is refusing communication from comcast.net. Unfortunately, we wouldnt know what type of filtering they are using to block the email traffic and you will need to try to reach out to the IT contact/Network Administrator for unica.it for further resolution.

[Old_Professor]

It turns out that unica.it was blocking Comcast. They unblocked it upon my friend's request.