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A client recently switched to Exchange Server / Outlook for their email. Since then emails from my company to any email address at their company bounce back from the System Administrator with this error:

  Your message did not reach some or all of the intended recipients.

   Subject:  Email Solution
   Sent: 12/12/2012 11:08 AM

   The following recipient(s) cannot be reached:

   '' on 12/12/2012 11:08 AM
    550 5.1.1 <> recipient rejected

Looking in the Message Options of the bounce back email shows no data in the Internet Header field.

My client's IT guy says we're not being blocked, but I cant think of any other reason the bounce would occur.

Any suggestions on what questions to ask or how to fix this would be helpful.

I'm using a desktop version of Outlook 2007 and connecting through my ISP.


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Of course you're not being blocked because the NDR states "recipient rejected", not "sender rejected". I can think of a few things that might be wrong (on the recipient's end): 1. The recipient's server isn't authoritative for the domain you're sending to. 2. The recipient doesn't have the email address that you're sending to. 3. Some other configuration error on the recipient's end. – joeqwerty Dec 12 '12 at 22:53
Thank you joeqwerty. I'll check with their admin on point 1. Regarding point 2, I get the same bounce when they send an email and I hit "reply to"... and they have no problem sending/receiving internally, so the address must be in their system...right? I am no expert in exchange, I appreciate your guidance. – Stan Dec 12 '12 at 23:10
Did the MX record change for your client? I've seen similar errors (although User Unknown errors) where the sender had stale DNS records and was attempting to resolve their MX to an IP that no longer hosted it. If this is the case that would mean that your DNS records are stale and need to be refreshed. – DKNUCKLES Dec 12 '12 at 23:58
@Stan - That sounds about right. If you're replying to an email then the recipient email address should be OK. It may be a problem with DNS (the MX record) as DKNUCKLES stated or it may be a problem with the Exchange configuration. If the Accepted Domains in Exchange is incorrectly configured then internal to internal email would work but external to internal email would not. – joeqwerty Dec 13 '12 at 0:10
@DKNUCKLES - thank you for your help. I'll follow up and see if we can find a resolution. – Stan Dec 13 '12 at 16:37

550 5.1.1 means that the recipient email server believes that the email address does not exist at the destination domain, and therefore has no way to deliver it.

Unless you simply made a typo in the email address, this is not something that you can fix, and must be addressed at the other end.

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It may also be rejected for policy reasons, e.g. because the server is configured to not accept mail for that combination of sender and recipient addresses. – Jenny D May 14 '13 at 9:29
@JennyD If that's the case, then the mail server is blatantly lying about the rejection reason. Which isn't helpful to anyone. – Michael Hampton May 14 '13 at 13:17
RFC5321 §7.9 "When mail is rejected for these or other policy reasons, a 550 code SHOULD be used in response to EHLO (or HELO), MAIL, or RCPT as appropriate." I'll agree that it's not helpful, though. – Jenny D May 14 '13 at 13:43
@JennyD Wrong RFC. This is an RFC 3463 extended status code. Where, 5.1.1 means "user doesn't exist" and 5.7.1 means "I don't want your junk, go away". – Michael Hampton May 14 '13 at 13:49
You make me very happy that I'm not longer having email systems as a major part of my job. – Jenny D May 14 '13 at 13:51

Tell the IT guy to add the following records to their domain DNS Zone file supposing that their domain is

A record

Host: mail

Points to: [put here the ip address of without brakets]

MX record

Priority: 0

Host: @

Points To:

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A Spam filter may also be the cause if emails are passing through it and the email address is not registered on it as yet

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