Recently, senders from Hotmail have begun to get the following NDR when trying to e-mail our domain.

EDIT : Full NDR Message

Action: failed Status: 5.5.0 Diagnostic-Code: smtp;550-Please turn on SMTP Authentication in your mail client, or login to the 550-IMAP/POP3 server before sending your message. 550-snt0-omc3-s36.snt0.hotmail.com []:49271 is not permitted to 550 relay through this server without authentication

This is seemingly out of the blue and I'm at a loss as to why this is happening.

Pertinent Information

  • We have multiple domains hooked up to our Exchange server. We changed our company name in January of this year, and the old primary domain (olddomain.com) will accept e-mails from Hotmail accounts, however e-mails sent to the new primary domain (newdomain.com) bounce back with the NDR listed above.
  • The bounces only appear to be happening when the Hotmail sender is sending a new e-mail, and not if they are responding to an e-mail sent from our end.
  • We have made no changes to the configuration of our server recently. This e-mail first appeared last Friday.
  • As far as I can tell, the mail doesn't even seem to get to our server
  • We performed an Exchange 2003 to 2010 migration last year. The 2003 acts as a Smart Host

Any advice on this issue would be greatly appreciated! I'm at a loss

  • When you send an email message from your hotmail account, in the bounced message, what is the ip address and name of the SMTP server that is rejecting your message?
    – Greg Askew
    Jun 18, 2012 at 16:24
  • Edited question with full NDR method.
    Jun 18, 2012 at 16:58
  • Is it absolutely only hotmail which fails? All others are coming in fine? Really strange...
    – MichelZ
    Jun 18, 2012 at 17:45
  • Hotmail is the only domain I've identified / has been brought to my attention. All other external e-mail works as it should
    Jun 18, 2012 at 17:45
  • Just to be sure, can you try testexchangeconnectivity.com If that really works, I think you have to open a case with Microsoft/Hotmail to further troubleshoot
    – MichelZ
    Jun 18, 2012 at 17:47

3 Answers 3


Is your Exchange Server configured to be autoritative for this Domain?

Hub Transport -> Accepted Domains

  • No it is not. The only authoritative domains are the ones that we own.
    Jun 18, 2012 at 17:23
  • 1
    This is what I mean. your olddomain.com and your newdomain.com are listed here?
    – MichelZ
    Jun 18, 2012 at 17:32
  • Yes both domains are listed there. I apologize for confusion. The odd part here is that olddomain.com is listed as the default, but e-mails are leaving the organization as newdomain.com
    Jun 18, 2012 at 17:41
  • The Settings on the individual user decides on what Domain to send as. (the bold SMTP address).
    – MichelZ
    Jun 18, 2012 at 17:44

We are in the same situation. We have Exchange 2010 in house, and recently found that Hotmail, MSN and Live e-mails are not deliverable to our domain. We get the same NDR that you have above. I also have another client with their mail hosted with Office 365 who has the same problem just with a slightly different NDR (the NDR still says relaying isn't allowed even though it shouldn't be relaying anything).

One thing we found is that this only seems to occur when the message is composed in the web mail page. If we send from Hotmail using a mail client or smartphone it works. Depending who is trying to e-mail you this may help work around the issue to some degree.

It seems like this is a bug with the Hotmail service and its web mail interface, but I don't know how to confirm that for sure. If it is a Hotmail problem we'll have to wait for MS to fix it.

  • Thank you for your insight on this! I've launched a ticket with Microsoft but have yet to hear back. If /when I do I'll post back.
    Jun 20, 2012 at 13:16
  • As of this morning this problem appears to be resolved. Never got any more insight from MS - but it's working which is the main thing. Jun 22, 2012 at 12:36

This information was provided elsewhere in a question because this question has been protected. If it is not applicable please flag it for deletion.

This error is based mostly on mobile devices, mostly on iPhones and mostly on mobile networks. This is how much I have narrowed it to.

I believe:

Hotmail checks where your are connecting from

  • If it is a mobile network
  • it requires additional security for sending messages
  • but the default iPhone config does not have this option for hotmail
  • if the user creates the hotmail account on the iPhone with SMTP AUTH enabled manually it might solve the situation

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