Exchange server 2010 on server 2012

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Hi Antonio Young

Thank you for posting your question in the Microsoft Q&A forum. 

Microsoft (Exchange Online Protection) is not blocking your mail due to an arbitrary “IP range rule”. The rejection occurs because Spamhaus has listed your specific IPv6 address or prefix. 

As long as your IP remains on a Spamhaus blocklist, Microsoft will reject your mail, even if your SPF, DKIM, and DMARC records are correctly configured. 

It’s important to note that Microsoft cannot override Spamhaus block decisions, nor can this be resolved through server-side configuration changes. 

To verify, you can use tools such as MX Lookup Tool - Check your DNS MX Records online - MxToolbox. 

Note: Microsoft is providing this information as a convenience to you. These sites are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please ensure that you fully understand the risks before using any suggestions from the above link. 

Only your hosting provider can request Spamhaus delisting for the affected IPv6 block. You will need to contact them directly to initiate removal. 

Additionally, be aware that Microsoft 365 caches Spamhaus blocklist results for several hours after removal. Even after Spamhaus delists your IP, Microsoft’s servers may continue to reject mail until the cached data expires.

For your references: 

Mail delivery issue - SpamHaus involved - Microsoft Q&A. 

Fix NDR error 550 5.7.1 in Exchange Online - Exchange | Microsoft Learn. 

I hope this information is helpful. 

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The error means the public IP address of the Exchange 2010 server (or outbound smart host) is listed on Spamhaus, so Exchange Online Protection (EOP) at mail.protection.outlook.com is rejecting the mail with 550 5.7.1 Service unavailable, client host [x.x.x.x] blocked using Spamhaus.

To fix this, the sending IP must be removed from the Spamhaus blocklist and the underlying cause of the listing addressed.

1. Identify the exact public IP that is sending mail
   • Check the NDR details or message headers for Client host [x.x.x.x].
   • Confirm that this is the IP your Exchange 2010 server uses to send outbound SMTP (or your firewall/SMTP relay IP).
2. Request delisting from Spamhaus
   • From a browser, go to the Spamhaus lookup/delist page and enter the public IP.
   • Follow Spamhaus’s instructions to request removal. They will usually indicate why the IP was listed (open relay, malware, spam volume, dynamic IP, etc.).
3. Fix the root cause before or immediately after delisting Typical issues to check on the Exchange 2010 side and network:
   • Make sure the server is not an open relay.
   • Check for compromised accounts or applications sending large volumes of mail.
   • Review outbound queues and message tracking logs for unusual volume or destinations.
   • Ensure antivirus/antimalware is up to date on the server.
   • If using a consumer/dynamic ISP line, move outbound mail to a proper static IP or a reputable SMTP relay/smart host.
4. Consider routing outbound mail through a trusted relay
   • If keeping the current IP clean is difficult (e.g., ISP reputation, shared IP), configure Exchange 2010 to send outbound mail via a smart host (such as your ISP’s or a third‑party mail relay) that has good reputation and proper anti‑abuse controls.
5. Verify after changes
   • After Spamhaus confirms delisting, send test messages to the affected domains.
   • Confirm no new NDRs with 550 5.7.1 ... blocked using Spamhaus are generated.

If instead the error text in the NDR mentions Microsoft’s own blocklist (for example, “Client host [x.x.x.x] blocked using Blocklist 1; To request removal from this list please forward this message to delist@microsoft.com”), follow the instructions in the NDR and send the full bounce message to delist@microsoft.com after ensuring the server is not sending spam.

References:

• Fix NDR error "550 5.7.1" in Exchange Online