emails are bouncing back when sending to yahoo

No way would they block outside email users. It wood make yahoo mail useless. And the error message would be different. What it shows now is that when the Microsoft SMTP server tries to connect to the Yahoo server there is a socket connection error, the kind of thing you'd get with a firewall blocking you, and it's not that.

I'm in the middle of business tech support work Microsoft on this and it's my impression they have no idea what it is. They have me fixing things that can't possibly be the problem. I pointed tech support to this thread to show site that I'm not the only one.

I am getting the exact message as "mpur" posted. From what I am reading am I to assume this error is really a YAHOO account issue. They must have changed some security feature on their accounts and they are blocking anyone that doesnt have a YAHOO account. I am a travel agent and all of my clients emails are bouncing back as undeliverable. It is not in their spam/junk folder. Please find a solution to this quickly. thanks!

I filed a support request with Microsoft.

FWIW, the support article mentioned (https://learn.microsoft.com/en-us/exchange/troubleshoot/email-delivery/send-receive-emails-socketerror) says to make registry changes on the on-prem server. I have no on-prem server. I'm connected directly to Office 365 for email services.

I'm getting the same errors, and only when I send email to yahoo.com:

1/13/2024 3:53:26 PM - Server at MN2PR13MB3870.namprd13.prod.outlook.com returned '550 5.4.300 Message expired -> 421 4.4.2 Connection dropped due to SocketError'
1/13/2024 3:52:24 PM - Server at mta5.am0.yahoodns.net (67.195.228.106) returned '421 4.4.2 Connection dropped due to SocketError'

I'm on Office Pro Plus 2016 using the desktop client, although it happens from the web client as well. My account is Microsoft 365 Business Basic.

I've tried sending to two different yahoo.com emails and I have sent at least 5 emails over 2 days.

The support article you listed presumes I'm using an old TLS version, but I'm using whatever Microsoft 365 supplies by default. Based on the fuller headers below, it's all TLS 1.2.

Original message headers:

Received: from CH0PR13MB5082.namprd13.prod.outlook.com (2603:10b6:610:ed::14)

 by MN2PR13MB3870.namprd13.prod.outlook.com (2603:10b6:208:1e9::20) with

 Microsoft SMTP Server (version=TLS1_2,

 cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7181.21; Sat, 13 Jan

 2024 13:59:18 +0000

Received: from MW5PR13MB5878.namprd13.prod.outlook.com (2603:10b6:303:1c9::5)

 by CH0PR13MB5082.namprd13.prod.outlook.com (2603:10b6:610:ed::14) with

 Microsoft SMTP Server (version=TLS1_2,

 cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7181.21; Sat, 13 Jan

 2024 02:55:19 +0000

ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none;

 b=DGeCf6TtbQRfJoqXMvaTrygs8ztPaSTX7pbbh7640MhFEsqRvZm5inAXsZ0aBCD0yqCPZ9vl+u+XzfSHdIm0B8xqfppBHPC0aqlDpDDZDAkF6ygttBjE2efHBCoyANaXLbsHC4VLOxZC8ve5v2AB8IEiUoIWxV7tAEyEsBAbn1jce4FTAC02ZgP0IAR16jFr36tlznqlt/F6tevE3uXI16GSGcu79YqM1oBmIeAqCQ5GAyliiz+PGrxvEDmqikuySULaZcoxt4gWlifNt/qn1GBxmQHEszveRzu2EKRkqkSzZ04ltElEb2hodRET+iEruR0YJMdWLJJGXreZhk1Tbw==

ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com;

 s=arcselector9901;

 h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1;

 bh=pmF0dHM+eqWtinvkBnN3FlkywqX3KfqXGO+QxEwFxAU=;

 b=Ifx401K/pquhV5LSao1qwLLDqDtd/Coitmvtb4jbeoMBQspquKabvFMTBcSeHMIkR5wr1nci+ZPP6vJ1hj/PEryFmNzYC7kOEIxp+a/ryXK9BYA8ScJzzPfu+P6Cr0YeDCVGvAOV6cEnzFX+93VGG4fGUtq8sAdVIL6ZIqnU9Y6pSuH6GGcJwHRIvDYFqBnM3jzPUU62s3i6DUQCfDFpkBc07xBoLB01jf7XG1wmFLfUkxLJ1C5RisSjTTER/TBZTZ1WESPJl4yj6rGU79jaYRuQirDU22XVUCdtU01jratZ8v0gdXkoRLVd2NaCfbCvpmHHNo5DCvT559MihRX7Tw==

ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass

 smtp.mailfrom=larryseltzer.com; dmarc=pass action=none

 header.from=larryseltzer.com; dkim=pass header.d=larryseltzer.com; arc=none

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;

 d=LarrySeltzer.onmicrosoft.com; s=selector2-LarrySeltzer-onmicrosoft-com;

 h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck;

 bh=pmF0dHM+eqWtinvkBnN3FlkywqX3KfqXGO+QxEwFxAU=;

 b=J6KTBOxh8gd/9BVQ1o4Wiz88qYhal/bam0GgmbrLfOn6jN0+ZSnl9OwnCa2Nbf5VcEFPgUfiJ6ksMpUPwYY//J0jIR9N1qEecNNUOPOcd3X7SVT8v0Mqqdf7KDZXyCzuY+vei2I+dRbG7yxZRHj72HAJzOGvi1lE9BikQQidIbw=

Received: from BLAPR13MB4578.namprd13.prod.outlook.com (2603:10b6:208:332::10)

 by MW5PR13MB5878.namprd13.prod.outlook.com (2603:10b6:303:1c9::5) with

 Microsoft SMTP Server (version=TLS1_2,

 cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7181.18; Fri, 12 Jan

 2024 15:52:35 +0000

Received: from BLAPR13MB4578.namprd13.prod.outlook.com

 ([fe80::bfc2:9102:248f:3ec9]) by BLAPR13MB4578.namprd13.prod.outlook.com

 ([fe80::bfc2:9102:248f:3ec9%5]) with mapi id 15.20.7181.018; Fri, 12 Jan 2024

 15:52:35 +0000

From: Larry Seltzer <******@larryseltzer.com>

To: Miranda Aaron <******@yahoo.com>

Subject: RE: did you get this?

Thread-Topic: did you get this?

Thread-Index: AQHaRW8l29TU3qmeL0CC3dpEwkx787DWU56g

Date: Fri, 12 Jan 2024 15:52:35 +0000

Message-ID: <******@BLAPR13MB4578.namprd13.prod.outlook.com>

References: <******@mail.gmail.com>

 <******@yahoo.com>

In-Reply-To: <******@yahoo.com>

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thank you