How it works

Mailbox flow and how inbound spam checking fits in.

Mailbox flow

Create user provisions mailbox system folders including x402.Pending (review queue) and x402.Spam (identified spam).
New inbound mail is checked against local message memory first. A strong INBOX-trust match short-circuits straight to INBOX.
Remote spam check runs when local memory does not already make the decision. verdict=notspam is delivered to INBOX; verdict=spam is filed to x402.Spam; verdict=uncertain and verdict=error are filed to x402.Pending for review.

How the email spam check works

The inbound checker sends only From, optional Reply-To, and a sanitized Subject to the configured remote email-spam-check endpoint. The body is not sent.

That remote service returns a structured verdict such as spam, notspam, uncertain, or error, which is stamped onto the message as X-CTJ-Spam-Check and then routed into the appropriate folder.

If local message memory already has enough confidence, the paid remote check is skipped. This keeps repeat-good mail flowing to INBOX without paying for the same decision over and over.

Inbound spam-check charges are paid by the service operator, not as a per-mailbox action on this page.

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