Init

backend/src/mail/newsletter.ts

@@ -0,0 +1,45 @@
+const headerIncludes = (headers: Map<string, string>, key: string) =>
+  headers.has(key.toLowerCase());
+
+const headerValue = (headers: Map<string, string>, key: string) =>
+  headers.get(key.toLowerCase()) ?? "";
+
+const containsAny = (value: string, tokens: string[]) =>
+  tokens.some((token) => value.includes(token));
+
+export const detectNewsletter = (params: {
+  headers: Map<string, string>;
+  subject?: string | null;
+  from?: string | null;
+}) => {
+  const subject = (params.subject ?? "").toLowerCase();
+  const from = (params.from ?? "").toLowerCase();
+  const headers = params.headers;
+
+  const hasListUnsubscribe = headerIncludes(headers, "list-unsubscribe");
+  const hasListId = headerIncludes(headers, "list-id");
+
+  const precedence = headerValue(headers, "precedence").toLowerCase();
+  const bulkHeader = headerValue(headers, "x-precedence").toLowerCase();
+
+  const headerHints = containsAny(precedence, ["bulk", "list"]) ||
+    containsAny(bulkHeader, ["bulk", "list"]) ||
+    headerIncludes(headers, "list-unsubscribe-post");
+
+  const subjectHints = containsAny(subject, ["newsletter", "unsubscribe", "update", "news", "digest"]);
+  const fromHints = containsAny(from, ["newsletter", "no-reply", "noreply", "news", "updates"]);
+
+  const score = [hasListUnsubscribe, hasListId, headerHints, subjectHints, fromHints].filter(Boolean).length;
+
+  return {
+    isNewsletter: score >= 2,
+    score,
+    signals: {
+      hasListUnsubscribe,
+      hasListId,
+      headerHints,
+      subjectHints,
+      fromHints
+    }
+  };
+};