Email sent rejected #550 5.7.1

I have user trying to send emails to
Delivery has failed to these recipients or distribution lists:
Your message wasn't delivered because of security policies. Microsoft
Exchange will not try to redeliver this message for you. Please provide the
following diagnostic text to your system administrator.

The following organization rejected your message:


Sent by Microsoft Exchange Server 2007

Diagnostic information for administrators:

Generating server: our transport server #550 5.7.1 Connections not accepted from servers without
a valid sender domain.flph259 Fix reverse DNS for x.x.x.x ##
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LLMorrissonConnect With a Mentor Commented:
You need to add a reverse lookup address to public DNS for your server, so that when the mail server does a reverse check on the IP you are connecting from it points to the name you claim to be.

Once that all matches up this problem will go away.

Alan HardistyConnect With a Mentor Co-OwnerCommented:
Please call your ISP and ask them to configure Reverse DNS on your Fixed IP Address as something like - this name needs to resolve in DNS back to the Fixed IP Address of your server.

My article explains a few more checks you need to make to make sure oyu are RFC Compliant:
Apologies I misread the error and see now that is not in fact your server but one of the remote MXs. Basic premise is still appropriate though, and Alan's article covers it off nicely.

Alan HardistyCo-OwnerCommented:
So 2 months after you couldn't be bothered to reply to the participating Experts you close it down with "This was resolved and by Network Engineers" and then you are able to ask new questions.

Objecting to arbitrary closure.
Alan HardistyCo-OwnerCommented:
50/50 Split between http:#a35095538 and http:#a35095572 should solve this problem happily.

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