Outlook is returning Remote Server returned '421 4.3.2 Service not available' for two of my groups.outlook.com groups

* * * Mod note: See the post by Diane Poremsky MVP * * *

Yesterday and today outlook.com is refusing all group email.
I have two different groups that I use weekly. Today I get this message.'

The recipient's email system isn't accepting messages now. Please try resending your message later or contact the recipient directly.

Generating server: BN6PR19MB0962.namprd19.prod.outlook.com
Total retry attempts: 4

___@___.___
Remote Server returned '421 4.3.2 Service not available'

Original message headers:

Received: from SA0PR19MB4412.namprd19.prod.outlook.com (2603:10b6:806:ba::17)
by BN6PR19MB0962.namprd19.prod.outlook.com (2603:10b6:404:74::9) with
Microsoft SMTP Server (version=TLS1_2,
cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.5373.18; Sun, 26 Jun
2022 19:00:06 +0000
Received: from DM4PR19MB6342.namprd19.prod.outlook.com (2603:10b6:8:a7::11) by
SA0PR19MB4412.namprd19.prod.outlook.com (2603:10b6:806:ba::17) with Microsoft
SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
15.20.5373.18; Sun, 26 Jun 2022 18:59:37 +0000
Received: from DM4PR19MB6342.namprd19.prod.outlook.com

WHAT IS GOING ON WITH OUTLOOK GROUPS??

I create a NEW group to test and it ALSO returns the same error.

* Pinned until August 1, 2022.