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I've had trouble receiving invoices from a sender's domain -- they use a 3rd party service when sending invoices. No problem with their regular emails, of course.
I resorted to weakening everything under "Settings spamprotection", and now I'm able to receive finally.
"Flag & Redirect" has been consistently set to "Junk", but nothing has ever appeared there. I assume that only applies to the content filter? (Something I'm only figuring-out now)
If so, that's a major concern, because there would be no way of knowing when a sender fails on Greylisting, SMTP Plausibility, or Real-time blacklist?
The same problem 
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