All the emails sent to us by our customer (email address removed for privacy reasons) arrive in our quarantine with an SCL score of 5.

However, the email address passes the DMARC tests perfectly (test carried out with https://www.dmarctester.com/).
The domain is not blacklisted, and emails from his colleagues email address removed for privacy reasons and email address removed for privacy reasons arrive with no problem.
The content of the email shouldn’t be the problem either, as an empty email is also quarantined.

What additional diagnostic work can I do to understand why the SCL for each of his emails scores 5?

​All the emails sent to us by our customer (email address removed for privacy reasons) arrive in our quarantine with an SCL score of 5. However, the email address passes the DMARC tests perfectly (test carried out with https://www.dmarctester.com/).The domain is not blacklisted, and emails from his colleagues email address removed for privacy reasons and email address removed for privacy reasons arrive with no problem.The content of the email shouldn’t be the problem either, as an empty email is also quarantined. What additional diagnostic work can I do to understand why the SCL for each of his emails scores 5?  Read More

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