Permanent error sending email to att.net and sbcglobal.net

@RickK1 

For me, this problem started yesterday.  I have a distribution list of about 75 names/email addresses.  I am getting permanent error on those email I try to send.

I also tried a couple just sent to specific individuals with att.net or sbcglobal.net addresses.  Those failed also.

Any idea why this is happening?

And, am i posting this in the wrong place?

What are the exact error messages you're getting, leaving out any personal identifying information, such as anything before the @ sign.

@Again 

Reporting-MTA: dns; resqmta-c1p-023461.sys.comcast.net [96.102.19.18]

Received-From-MTA: dns; resomta-c1p-022584.sys.comcast.net [96.102.18.233]

Arrival-Date: Mon, 19 Sep 2022 01:30:31 +0000

Final-recipient: rfc822; [Edited: "Personal Information"]

Diagnostic-Code: smtp; 553 5.3.0 flpd595 DNSBL:RBL 521< 96.102.19.42 >_is_blocked.For assistance forward this error to [Edited: "Personal Information"]

Last-attempt-Date: Mon, 19 Sep 2022 01:30:31 +0000

-----Original Message-----
From: [Edited: "Personal Information"] < [Edited: "Personal Information"]>
Sent: Sunday, September 18, 2022 8:31 PM
To: [Edited: "Personal Information"]
Subject: Permanent Error

      This is an automatically generated Delivery Status Notification.     

Delivery to the following recipients failed permanently:

   *xxxxxxxx@sbcglobal.net

Reason: Permanent Error

My husband and I had the same problem with addresses that previously worked - sbcglobal.net as well as snet.net and att.net.  All other recipients on the list went through.

We've reached out the destination domains involved, no other update yet.

There's a similar report at https://forums.xfinity.com/conversations/email/new-limit-on-email-exchanges/6328b97a48c60d55e60521f7, but no solution. Note that the IP address in the "DNSBL:RBL 521< 96.102.19.42 >_is_blocked" error message is assigned to a Comcast mail transfer agent (mail server). See https://postmaster.comcast.net/outbound-mail-servers.html.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

My problem seems to have resolved itself. Sent to distribution list today without issues.

I had the similar problem as Bruce mentioned.   I contacted AT&T and it turns out it was a problem on their end which they have now resolved. Hopefully it resolves this problem as well.