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
Remote Server returned '550 <email@example.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
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" <firstname.lastname@example.org>
Date: Tue, 20 Oct 2015 18:54:30 +0000
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.