Exchange server 2013 send email issue to external network

We have recently changed our ISP and we are facing the issue with exchange server sent emails.
all users are able to send internal emails and recevie emails externally too.

But when the send emails to external domain or network it gives below error.
Diagnostic information for administrators:
Generating server: MAIL.domain.com
user@domain.com
mx.domain.com
Remote Server returned '550 <user@domain.com> No such user here'
Original message headers:
Received: from MAIL.domain.com (10.0.0.8) by MAIL.domain.com
 (10.0.0.8) with Microsoft SMTP Server (TLS) id 15.0.775.38; Wed, 21 Oct 2015
 00:24:31 +0530
Received: from MAIL.domain.com ([fe80::2c25:f12b:592a:4d7c]) by
 MAIL.domain.com ([fe80::2c25:f12b:592a:4d7c%12]) with mapi id
 15.00.0775.031; Wed, 21 Oct 2015 00:24:31 +0530
From: "user1" <user1@domain.com>
To: user<user@xyz.com>
Subject: ateae
Thread-Topic: ateae
Thread-Index: AQHRC2jALYX6F1USs0yNfYYE8h1z5Q==
Date: Tue, 20 Oct 2015 18:54:30 +0000
Message-ID: <8b892d32bed240eead8351eee02d060f@MAIL.domain.com>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-originating-ip: [10.1.1.243]
Content-Type: multipart/alternative;
        boundary="_000_8b892d32bed240eead8351eee02d060fMAILrigelnetworkscom_"
MIME-Version: 1.0

For more info, we are using smart host and we have not make live our exchange server. we have configured third party tool to download  external emails.
we have configure local exchange IP port forwarding with live IP using sonicwall firewall.

We have tried to recreate send connector and restart transport service multiple times but no luck.
We can resolve our domain name with nslookup and it seems fine. but we are facing the issue with sent emails. our Production is down so quick response would be highly appreciated.

Kindly suggest...!!
rigelnetAsked:
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AlexantSystemsCommented:
The error message you are getting indicates that the your email server did talk to an external email server  but the recipient did not exist on the remote email server. Is this happing on all emails or did you try different email addresses such as ones located at outlook.com or gmail.com?
From the mail server telnet to port 25 on mx1.hotmail.com and type ehlo and publish the results back here.
If you do not have telnet installed on your Exchange server you can add it by going to Programs and Features in your Control Panel and click on Turn Windows features on or off on the left, click on Next till you get the Select Features screen, scroll down to Telnet Client and check the box and then click Install and follow the rest of the prompts.
To run the telnet command start a DOS session by right clicking the Start button and selecting Command Prompt (Admin) and then type in the telnet command
telnet mx1.hotmail.com 25
ehlo

Post the results of the telnet session here.
rigelnetAuthor Commented:
Below is the result of telnet mx1.hotmail.com 25 ehlo command. Also we have tried to send email to gmail but still the error is same.

220 BAY004-MC3F41.hotmail.com Sending unsolicited commercial or bulk e-mail to M
icrosoft's computer network is prohibited. Other restrictions are found at http:
//privacy.microsoft.com/en-us/anti-spam.mspx. Tue, 20 Oct 2015 17:12:31 -0700
ehlo
250-BAY004-MC3F41.hotmail.com (3.21.0.218) Hello [221.134.83.52]
250-SIZE 36909875
250-PIPELINING
250-8bitmime
250-BINARYMIME
250-CHUNKING
250-STARTTLS
250-AUTH LOGIN
250-AUTH=LOGIN
250 OK
Justin YeungSenior Systems EngineerCommented:
Received: from MAIL.domain.com (10.0.0.8) by MAIL.domain.com

the server that generating the error which looks like it is internal device?

what is your send connector pointing to? is it pointing to a spam filter that require user existing on the appliance? (ie, iron port)

or is that 10.0.0.8 ip the local exchange server? do you have cas/mailbox role on same box? or separated?

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AlexantSystemsCommented:
I have to agree with Justin, are you using some form of in-house SPAM filter to route you email out?
rigelnetAuthor Commented:
The issue was we need to allow live IP as a whitelist on our external server.
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