All external incoming mails are getting rejected!

Dear Sir/Madam,

This is with respect to w***********u.com domain for which mail services are provided by Zoho.

All the mails from GMail, Hotmail and other external mail providers are getting rejected. But the mails internally from Zoho (w***********u.com) accounts are getting delivered to w***********u.com accounts.

The mail gets rejected for all users. (*@w***********u.com) with error code 551 5.1.1. Invalid sender IP.

I have pasted the error logs below. Kindly help me rectify it asap.

We are missing many important mails due to this.

Thanks and Regards

Ashwin

+91-96000xxxx0

ERROR MESSAGE FROM GMAIL

Message not delivered

There was a problem delivering your message to xxxx@w***********u.com. See the technical details below, or try resending in a few minutes.

The response from the remote server was:

551 5.1.1 <xxxx@w***********u.com> Invalid Sender IP

Final-Recipient: rfc822; xxxx@w***********u.com
Action: failed
Status: 5.1.1
Remote-MTA: dns; mx.zoho.com. (204.141.32.121, the server for the domain w***********u.com.)
Diagnostic-Code: smtp; 551 5.1.1 < xxxx@w***********u.com> Invalid Sender IP
Last-Attempt-Date: Wed, 03 Jan 2018 00:44:32 -0800 (PST)

ERROR MESSAGE FROM HOTMAIL

mx.zohomail.com rejected your message to the following email addresses:

xxxx@w***********u.com (xxxx@w***********u.com)
The address you sent your message to wasn't found at the destination domain. It might be misspelled or it might not exist. Try to fix the problem by doing one or more of the following:

Send the message again, but before you do, delete and retype the address. If your email program automatically suggests an address to use, don't select it.
Clear the recipient AutoComplete cache in your email program by following the steps in this article: Status code 5.1.1. Then resend the message, but before you do, be sure to delete and retype the address.
Contact the recipient by some other means (by phone, for example) to confirm you're using the right address. Ask them if they've set up an email forwarding rule that could be forwarding your message to an incorrect address.

mx.zohomail.com gave this error:
<xxxx@w***********u.com> Invalid Sender IP

Diagnostic information for administrators:

Generating server: BO1IND01HT007.mail.protection.outlook.com

xxxx@w***********u.com
mx.zohomail.com
Remote Server returned '551 5.1.1 <xxxx@w***********u.com> Invalid Sender IP'

Original message headers:

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=hotmail.com;
 s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version;
 bh=HkaQnVOfx/A0SfA8ZPf0zklRaKtDD9fCuhIRm4qQMlg=;
 b=
Received: from BO1IND01FT006.eop-IND01.prod.protection.outlook.com
 (10.152.202.54) by BO1IND01HT007.eop-IND01.prod.protection.outlook.com
 (10.152.202.151) with Microsoft SMTP Server (version=TLS1_2,
 cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384) id 15.20.345.12; Wed, 3
 Jan 2018 08:50:06 +0000
Received: from BM1PR0101MB1313.INDPRD01.PROD.OUTLOOK.COM (10.152.202.52) by
 BO1IND01FT006.mail.protection.outlook.com (10.152.202.92) with Microsoft SMTP
 Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id
 15.20.345.12 via Frontend Transport; Wed, 3 Jan 2018 08:50:06 +0000
Received: from BM1PR0101MB1313.INDPRD01.PROD.OUTLOOK.COM
 ([fe80::4892:d17c:874f:4420]) by BM1PR0101MB1313.INDPRD01.PROD.OUTLOOK.COM
 ([fe80::4892:d17c:874f:4420%17]) with mapi id 15.20.0366.009; Wed, 3 Jan 2018
 08:50:06 +0000
From: XXXX X <xxxx@hotmail.com>
To: "xxxx@w***********u.com" <xxxx@w***********u.com>
Subject: Test
Thread-Topic: Test
Thread-Index: AQHThG/Z5rPZmTZj/UqLTaaSCwa/jQ==
Date: Wed, 3 Jan 2018 08:50:06 +0000
Message-ID: <BM1PR0101MB13132F7D81593140CA08F0FB9E1E0@BM1PR0101MB1313.INDPRD01.PROD.OUTLOOK.COM>
Accept-Language: en-IN, en-US
Content-Language: en-IN
X-MS-Has-Attach:
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x-ms-exchange-messagesentrepresentingtype: 1
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x-incomingheadercount: 44
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 (UTC)
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