The Fastmail help documentation doesn’t provide a comprehensive list of header values. Maybe you can submit a ticket and ask Fastmail support for a list? Here are the ones I’ve found by trolling through message headers:AccountsAlertsCommercialCommunityPurchasesSpamA sample rule could look like:If *any* of the following conditions apply *A header called* x-me-vscategory *contains* commercial *Move to* (or *Apply label* or whatever) …