Zimbra behind LibraESVA: SPAM false positives

A customer recently migrated their email security solution to LibraESVA. Since when I upgraded the Zimbra server I noticed our mails to the customer were wrongly reported as spam messages, but I was pretty sure our servers were well configured for being trusted.

A quick search showed SpamAssassin was failing DMARC test, this probably (I don’t know exactly how it works, unfortunately) LibraESVA is tampering with the email header.

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