Sometimes mails get flagged as spam even when it's not, this depends on the messages and the domain. Don't worry, the mails aren't instantly deleted, instead it goes to Spam Quarantine.
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Navigate to dashboard and click on Spam Quarantine under Incoming tab.

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Using Query Rules, quarantined mails should show up automatically.
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Checklist the false-positive mails you'd like to take action, hit Apply to execute the action.
