I can not send emails to yahoo accounts

Did you resplve this issue as I also can send to anyone but Yahoo?

Domain name is ppshr.co.uk

Does that shed any light on the problem? I hope so!

I am also having the same issue as the several other posters. It is mostly Yahoo.com email addresses, and the return error comes in sometimes 24-36 hours later.

Delivery has failed to these recipients or groups:

Diane Kxxxxxxx (******@yahoo.com)
Your message couldn't be delivered. Despite repeated attempts to contact the recipient's email system it didn't respond.

Contact the recipient by some other means (by phone, for example) and ask them to tell their email admin that it appears that their email system isn't accepting connection requests from your email system. 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.

For more information and tips to fix this issue see this article: https://go.microsoft.com/fwlink/?LinkId=389361.

Diagnostic information for administrators:

Generating server: DS0PR11MB8206.namprd11.prod.outlook.com
Total retry attempts: 8

******@yahoo.com
Remote server returned '550 5.4.300 Message expired -> 451 [RL01] Message temporarily deferred'

Original message headers:

Received: from DM4PR11MB5996.namprd11.prod.outlook.com (2603:10b6:8:5f::14) by
 DS0PR11MB8206.namprd11.prod.outlook.com (2603:10b6:8:166::5) with Microsoft
 SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 15.20.7386.13; Sat, 9 Mar 2024 15:53:53 +0000
Received: from DS0PR11MB6422.namprd11.prod.outlook.com (2603:10b6:8:c6::21) by
 DM4PR11MB5996.namprd11.prod.outlook.com (2603:10b6:8:5f::14) with Microsoft
 SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 15.20.7386.8; Sat, 9 Mar 2024 04:50:58 +0000
Received: from DM6PR11MB4546.namprd11.prod.outlook.com (2603:10b6:5:2a7::24)
 by DS0PR11MB6422.namprd11.prod.outlook.com (2603:10b6:8:c6::21) with
 Microsoft SMTP Server (version=TLS1_2,
 cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7386.6; Sat, 9 Mar
 2024 02:27:21 +0000
ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none;
 b=Z4u7kPr6Opq8UZw2BY6lB+KT5XIbA3vPrI92kYEohi4fM5JCZdFsJXq6SjOqpDOG+VQoD+ftGzkVsTyn/wCriFges2uwYZGyPVHwvS4qfXomnGnmHjrsXcgQsNUuQk+VqTDDemL7qeKM/kMtp2BvnQIRGN0JIV+4UX3k3JBIp1bsdJzI9HtmtId0O4iVcuQDxQok2uQE7hchJnu98YUR5DqpfclZwQgrA1DAxKJB/JoxvKPuS5AapqvyJA66BEW7SLFT9nrniB5kjNR5c2DITY+v7r//PsoLt1H/9xO8WGvonrV6TjxbmbRS1oZQB0zIy8WrwZWSS5aHgVL/Q4F4HA==
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=1or4a7xTPkA1fSDuAzZtHdALpuulRXFdGBaMK+W8qhY=;
 b=WcbEiTUh3fNeq8GQo6KPPlnpWP8fhHkkcGS3kcr8J1oXzC6jJumhlQ8YIiTBVw+3Ql5NYtsehtJr6ALG41c9gX8YCkBDRDH6tSKvUSii/4qE3KajjN5F8PsEIPwNBCYNhV2EwrQ0Y/nbeFDIXvyz/3pz1WUfLs40MzP7ttlWdUkh3qg+hOgbKgNhO/7EjTd4fkVB2XDiyOfOhHfsS/OkoPn2AC7cW7Q+zgPLaoKmBWR4ldEKlVaFlOqV1srcym4mTwivPrK+L/vNEE64Uje8JNJKrg66VljdKG5ARL3M0NrEEJ/MMFmcus9Y9b4mIXlBrsIjTsArRjxeavfMuO9CzA==
ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass
 smtp.mailfrom=libertytaxglendora.com; dmarc=pass action=none
 header.from=libertytaxglendora.com; dkim=pass
 header.d=libertytaxglendora.com; arc=none
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=NETORG3143950.onmicrosoft.com; s=selector2-NETORG3143950-onmicrosoft-com;
 h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck;
 bh=1or4a7xTPkA1fSDuAzZtHdALpuulRXFdGBaMK+W8qhY=;
 b=GLhcTzLLXR3HL8YAmlI5/9B87utdKFvjVERqP/dQW9ZJgJEhvLHw2nQAL5/i+DrTBoqFDOYyuFG6b++M1EGFxzxQoB756YspOJ8z3408Zekc4eHlOPBJNsb314NNk7KP8lFQWZRWvMgXBLW6iyUvWQAGwXHVBGFU+I5Dr70nhxg=
Received: from SN7PR11MB6995.namprd11.prod.outlook.com (2603:10b6:806:2ae::11)
 by DM6PR11MB4546.namprd11.prod.outlook.com (2603:10b6:5:2a7::24) with
 Microsoft SMTP Server (version=TLS1_2,
 cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7386.9; Fri, 8 Mar
 2024 22:04:14 +0000
Received: from SN7PR11MB6995.namprd11.prod.outlook.com
 ([fe80::317e:472:f8e:1eaf]) by SN7PR11MB6995.namprd11.prod.outlook.com
 ([fe80::317e:472:f8e:1eaf%7]) with mapi id 15.20.7339.009; Fri, 8 Mar 2024
 22:04:14 +0000

What is your domain name? Do not post the entire email address.

If you use custom domain name for your business, check your DNS records (SPF, DMARC etc).