Send Mail Broken on All Version of Outlook

About 2 weeks ago, sending mail with Outlook 2016 stopped working. First symptom was mail stuck in Outbox. Several sessions with Chat proved useless, as I knew more about Windows, Outlook and mail protocols than all of the technicians which I consider troublesome. I did go through the drills and changed mail server configurations:

pop.cox.net (Incoming)  Port: 995 (SSL)

smtp.cox.net (Outgoing) Port: 465 (SSL)

Errors posted are either of the following:

Your outgoing (SMTP) email server has reported an internal error. If you continue to receive this message, contact your server administrator or Internet service provider (ISP). The server responded: 552 5.2.0 g26C1x00S12WBbz0126EXe This message was undel.

The following recipient(s) cannot be reached:

 'xxxxx@cox.net' on 4/29/2018 9:23 PM

552 5.2.0 gRP51x00A4Ti44G01RP68d This message was undeliverable. This message has been found to be a potential spam message, and has therefore been blocked. Please visit http://ww2.cox.com/coxagainstspam for more information.

The last response from COX mail server is troubling, since mail sent to myself is considered Spam.

Have other COX users encountered this Draconian error and message? I used Outlook mail client successful on Cox for more than a decade, so I'm perplexed that this is occurring and COX technicians seem clueless. Further, the message at the URL in the last message seem more a Spam editorial than technical procedures to fix the broken mail system. I'm a very frustrated COX customer and am considering an alternative.