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40628 is not permitted to relay 550 - Error


I'm trying to e-mail one of my clients who's on a Hosted exchange platform we resell. It was working fine two days ago when i set it up for the client, however, now, when i try and e-mail it (from OWA), every other address is working but when i e-mail him i get the followign NDR...

Generating server: MAS-SERVER.masgroup.local
ns1.mas-host.com #550-Please turn on SMTP Authentication in your mail client, or login to the 550-IMAP/POP3 server before sending your message. mail.mas-design.co.uk 550-(remote.mas-group.co.uk) [IP]:40628 is not permitted to relay 550 through this server without authentication. ##
Original message headers:

Received: from MAS-SERVER.masgroup.local ([fe80::183b:f2d8:3283:c136]) by
 MAS-SERVER.masgroup.local ([fe80::183b:f2d8:3283:c136%10]) with mapi id
 14.01.0438.000; Fri, 21 Mar 2014 11:08:30 +0000
From: name <address>
To: name <address>
Subject: RE: OWL Solar Login
Thread-Topic: OWL Solar Login
Thread-Index: AQHPQ6RV4BVuCqgxu0CTbkYrpJHskJrrYgUAgAAB31c=
Date: Fri, 21 Mar 2014 11:08:29 +0000
Message-ID: <D00F390572D1A348A81048199611E3585C91967D@MAS-SERVER.masgroup.local>
References: <CF4F9697.1E209%address>,<CF51CB68.2973C%address>
In-Reply-To: <CF51CB68.2973C%address>
Accept-Language: en-GB, en-US
Content-Language: en-GB
x-originating-ip: []
x-tm-as-product-ver: SMEX-
x-tm-as-result: No--50.834500-5.000000-31
x-tm-as-user-approved-sender: No
x-tm-as-user-blocked-sender: No
Content-Type: multipart/alternative;
MIME-Version: 1.0
1 Solution
Arjun VyavahareTechnical ConsultantCommented:

Refer below article in which solution is provided:


I hope this will resolve your issue.

Andy MIT Systems ManagerCommented:
If I understand correctly it's just the one email account on this server that is having this issue and you can send emails fine to other users on the server? If this is the case I find it unlikley the smtp settings on your email client would be the issue.

Has the account got any sort of forward on it to another external email? I've seen this happen if the server tries to forward the original email to another server and it's the other server that's throwing the bounceback because it's trying to relay.

Also check transport logs, see f the client has any rules setup in Outlook, etc.
Simon Butler (Sembee)ConsultantCommented:
That isn't an Exchange error.
Therefore the most likely cause is something with the recipient - wrong server in the DNS records for example. It could be an error by the hosting company, who have put a server designed for use by their own customers to send email in the pool for inbound email.

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