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Exchange Troubleshooting

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#550 5.7.1 Message rejected as spam by Content Filtering

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Symptom:

Some messages are not being received and are being bounced with the message:

intended-recipient@example.com (Undelivered): 550 5.7.1 Message rejected as spam by Content Filtering.

where "intended-recipient@example.com" is the email address of the recipient on your exchange server.

Cause:

For some reason the message is being rejected by Content Filtering in Exchange.

Microsoft don't give details on what triggers the Content Filter to block emails, so you may never know exactly why an email was blocked by the Content Filter.

These notes assume that the email is good and shouldn't be blocked.

If you are the sender and don't have access to the configuration on the recipient's exchange server then all you can do is make a guess at which words or phrases might be triggering a negative score for the email or contact the exchange server administrator and ask for their help (point them to these notes should help).

Possible Remedies:

• Disable Exchange Content Filtering. This isn't desirable because it would open the flood gates to spam, so I'm not going to cover it further. Even if you use an external filtering service, disabling Exchange's filtering is still a bad idea.
• Change Content Filter settings to not reject, so email goes in recipients Junk items instead of the email being rejected.
  1. Open Exchange Management Console
  2. Navigate down to Microsoft Exchange On-Premises > Organization Configuration > Hub Transport.
  3. Open the "Anti-spam" tab.
  4. Right click on "Content Filtering" and select "Properties".
  5. Select the "Action" tab.

     This is where you configure what to do with emails that are flagged as spam.

  6. Clear the check box next to "Reject messages with SCL rating greater than or equal to ...".

     The email will still be regarded as junk, but will now appear in the recipient's junk email folder instead of being rejected.

     Note: If you have "Reject messages ..." cleared then clear "Delete messages ..." as well.

• Whitelist the sender.

  Annoyingly the Content Filter in Exchange Management Console doesn't provide the option to whitelist a sender. Yet you can whitelist a sender - details are here: How to add sender exceptions to content filtering. This method doesn't require any changed to the "Content Filtering" settings.

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These notes have been tested with Exchange Server 2010.