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

*** Email address is removed for privacy ***
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.

I don’t know what’s going on.

Actually, today my group email went through and delivered the email.

Marina Bermoy

I did the same. The new group seems to work, at least for some members, but each time I send I get :

Delivery has failed to these recipients or groups:

******@mts.outlook.com
Your message couldn't be delivered. The Domain Name System (DNS) reported that the recipient's domain does not exist.

Contact the recipient by some other means (by phone, for example) and ask them to tell their email admin that it appears that their domain isn't properly registered at their domain registrar. Give them the error details shown below. It's likely that the recipient's email admin is the only one who can fix this problem.

I have no idea what this email address is; it certainly isn't part of my group.

I created a new group tpo mirror my original group, whicg recently refused to allow access to members so I can't see them, let add or delete members!

The new group seems to work, at least for some members, but each time I send I get :

Delivery has failed to these recipients or groups:

******@mts.outlook.com
Your message couldn't be delivered. The Domain Name System (DNS) reported that the recipient's domain does not exist.

Contact the recipient by some other means (by phone, for example) and ask them to tell their email admin that it appears that their domain isn't properly registered at their domain registrar. Give them the error details shown below. It's likely that the recipient's email admin is the only one who can fix this problem.

I have no idea what this email address is; it certainly isn't part of my group.

I had to recreate my group to solve the visibility problem.

Abandoned the old group.