If content or transport filtering is triggered, the code appears in uppercase letters on the
x-pstn-settings line. If filtering isn’t triggered, the codes appear in lowercase letters.
The scores for these categories appear on the levels line, FC:95.5390 LC:95.5390. As with the other categories, filtering trigger when their scores drop below 85. In this case, neither triggered, so they appear in lowercase on the settings line.
The score for legal content category appears levels line, LC: 0.1839. The score is less than 85, which triggers the category. Because this category was triggered and because the legal-content filter was set to the highest value, the effective threshold on the settings line was set to zero (1.0000:0.0000). The effective threshold is compared to the spam score. If the spam score is less than the effective threshold, the message is spam. In this example, the spam score and effective thresholds are both zero, so the message is considered valid and is passed through to the recipient inbox.
The lt code on the settings line indicates that the legal transport category was turned on, but not triggered (would be
LT if triggered). The transport categories are not assigned numeric scores and don’t appear in the
X-pstn-levels line.
The General Transport Heuristics engine analyzes both the contents of a message as well as the source of the message. Senders of ~100% valid email will be given a bias against being quarantined as spam. These “trusted senders” are not added to a white list. These senders will continue to be subject to spam filters, but the general transport heuristic will lower the risk that email from valid senders might be accidentally quarantined.
If one of the general transport heuristic categories triggers, it will show up like any other category in the X-pstn-settings header with a GT1, GT2, or GT3. “GT” stands for “General Transport” and the three categories indicate their level of trust with GT1 being the most trusted. Each of the levels has an assigned multiplier that adjusts the spam threshold based on their level of trust. If a General Transport heuristic has been triggered, the “GT” will be capitalized.
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