diff --git a/.gitignore b/.gitignore
index 117c18b..9ab5d28 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,6 @@ dist/
 server/data/
 .vite/
 coverage/
+
+# Worktrees used by parallel agents; never part of a commit.
+.claude/worktrees/
diff --git a/FEATURES.md b/FEATURES.md
index f388498..f78ce3e 100644
--- a/FEATURES.md
+++ b/FEATURES.md
@@ -261,6 +261,18 @@ same query string — so what it builds can be read, edited and learned from.
 - **Show original**, **Show headers**, **Download (.eml)** and **Print**.
 - **Unsubscribe** where the message carries `List-Unsubscribe`.
 - **Sender details** expand to the full From/To/Cc/Reply-To with addresses.
+- **What the spam filter said** sits in those details, read back off the
+  message rather than scored here: the verdict, the score, the threshold it was
+  measured against, and the rules that moved it, largest mover first and signed
+  so which way each pushed is visible. Both the SpamAssassin-shaped `X-Spam-*`
+  set that Stalwart's own filter writes and Rspamd's `X-Spamd-Result` are read;
+  anything else is left alone rather than guessed at. Two things it will not
+  do: a score is always given the threshold it was measured against, because
+  6.7 is damning against 5 and unremarkable against 15 and the number alone is
+  not something a reader can act on — where no threshold was stated, it says
+  so; and where the filter recorded no verdict, none is invented from the score,
+  since the filter applies policy ihasmail cannot see. Mail that arrived without
+  these headers shows nothing.
 - **Message body theming** is off by default — sender HTML is left exactly as it
   was designed, on a light card. One setting lets mail that brings no colours of
   its own follow the app's theme instead.
diff --git a/server/src/mock/index.ts b/server/src/mock/index.ts
index 9fe22dd..3ccd56c 100644
--- a/server/src/mock/index.ts
+++ b/server/src/mock/index.ts
@@ -128,6 +128,14 @@ function addEmail(o: { from: [string, string]; to?: string; subject: string; day
     bodyStructure: { partId: null, blobId: null, size: 0, type: "multipart/mixed", name: null, charset: null, disposition: null, cid: null, subParts: [{ partId: "1", blobId: textBlob, size: text.length, type: "text/plain", name: null, charset: "utf-8", disposition: null, cid: null }, ...(o.html ? [{ partId: "2", blobId: htmlBlob, size: html.length, type: "text/html", name: null, charset: "utf-8", disposition: null, cid: null }] : []), ...attachments] },
     "header:List-Unsubscribe:asText": o.from[1].includes("newsletter") ? "<mailto:unsub@newsletter.example?subject=unsubscribe>, <https://newsletter.example/unsub>" : null,
     "header:X-Priority:asText": o.subject.startsWith("Security") ? "1 (Highest)" : null,
+    // Stalwart's spam filter writes the SpamAssassin-shaped set at delivery, so
+    // delivered mail carries it and mail this account wrote does not.
+    "header:X-Spam-Status:asText":
+      o.mailbox === "junk"
+        ? "Yes, score=14.2 required=5.0 tests=[BAYES_99=3.5, URIBL_BLOCKED=2.7, HTML_IMAGE_ONLY=1.4, SUBJ_ALL_CAPS=1.2, FROM_FREEMAIL=0.4] autolearn=no"
+        : o.mailbox === "inbox"
+          ? "No, score=-1.8 required=5.0 tests=[BAYES_00=-1.9, DKIM_VALID=-0.7, SPF_PASS=-0.1, HTML_MESSAGE=0.9]"
+          : null,
   };
   emails.push(e);
   return e;
diff --git a/web/src/lib/__tests__/spamScore.test.ts b/web/src/lib/__tests__/spamScore.test.ts
new file mode 100644
index 0000000..8aee66c
--- /dev/null
+++ b/web/src/lib/__tests__/spamScore.test.ts
@@ -0,0 +1,107 @@
+import { describe, expect, it } from "vitest";
+import { spamReport } from "@/lib/spamScore";
+
+const sa = (v: string) => spamReport({ "header:X-Spam-Status:asText": v });
+const rs = (v: string) => spamReport({ "header:X-Spamd-Result:asText": v });
+
+describe("spamReport, SpamAssassin-shaped headers", () => {
+  it("reads the verdict, score, threshold and tests", () => {
+    const r = sa("Yes, score=6.7 required=5.0 tests=[BAYES_99=3.5, HTML_MESSAGE=0.001, URIBL=2.2] autolearn=no");
+    expect(r).not.toBeNull();
+    expect(r!.verdict).toBe("spam");
+    expect(r!.score).toBe(6.7);
+    expect(r!.threshold).toBe(5);
+    expect(r!.source).toBe("spamassassin");
+    // Biggest mover first, so the reason it was scored reads off the top.
+    expect(r!.rules.map((x) => x.name)).toEqual(["BAYES_99", "URIBL", "HTML_MESSAGE"]);
+  });
+
+  it("reads a negative score and a clean verdict", () => {
+    const r = sa("No, score=-2.6 required=5.0 tests=[BAYES_00=-1.9, DKIM_VALID=-0.7]");
+    expect(r!.verdict).toBe("clean");
+    expect(r!.score).toBe(-2.6);
+    expect(r!.rules[0]).toEqual({ name: "BAYES_00", score: -1.9 });
+  });
+
+  it("survives a folded header, which is how they arrive", () => {
+    const r = sa("Yes, score=6.7\n\trequired=5.0 tests=[BAYES_99=3.5,\n\tURIBL=2.2]");
+    expect(r!.score).toBe(6.7);
+    expect(r!.rules).toHaveLength(2);
+  });
+
+  it("keeps a verdict that states no score, and a score that states no verdict", () => {
+    expect(sa("Yes")!.verdict).toBe("spam");
+    expect(sa("Yes")!.score).toBeNull();
+    const scoreOnly = sa("score=1.2 required=5.0");
+    expect(scoreOnly!.verdict).toBeNull();
+    expect(scoreOnly!.score).toBe(1.2);
+  });
+
+  it("says nothing when there is nothing it understands", () => {
+    expect(sa("")).toBeNull();
+    expect(sa("something else entirely")).toBeNull();
+    expect(spamReport({})).toBeNull();
+  });
+
+  it("drops a malformed test rather than scoring it as zero", () => {
+    const r = sa("Yes, score=3.0 tests=[GOOD=1.0, BROKEN=, =2.0, ALSO_GOOD=2.0]");
+    expect(r!.rules.map((x) => x.name)).toEqual(["ALSO_GOOD", "GOOD"]);
+  });
+});
+
+describe("spamReport, Rspamd", () => {
+  it("reads the action, score, threshold and rules with their notes", () => {
+    const r = rs("default: False [1.20 / 15.00]; MIME_GOOD(-0.10)[text/plain]; DKIM_ALLOW(-0.20)[example.com]; SUBJ_CAPS(2.00)[]");
+    expect(r!.verdict).toBe("clean");
+    expect(r!.score).toBe(1.2);
+    expect(r!.threshold).toBe(15);
+    expect(r!.source).toBe("rspamd");
+    expect(r!.rules[0]).toEqual({ name: "SUBJ_CAPS", score: 2 });
+    expect(r!.rules.find((x) => x.name === "DKIM_ALLOW")?.detail).toBe("example.com");
+    // An empty bracket is not a note.
+    expect(r!.rules[0]!.detail).toBeUndefined();
+  });
+
+  it("treats the acting verdicts as spam and False as clean", () => {
+    expect(rs("default: True [20.00 / 15.00];")!.verdict).toBe("spam");
+    expect(rs("default: reject [20.00 / 15.00];")!.verdict).toBe("spam");
+    expect(rs("default: add_header [16.00 / 15.00];")!.verdict).toBe("spam");
+    expect(rs("default: False [1.00 / 15.00];")!.verdict).toBe("clean");
+  });
+
+  it("declines to call greylisting a verdict about the message", () => {
+    const r = rs("default: greylist [8.00 / 15.00];");
+    expect(r!.verdict).toBeNull();
+    expect(r!.score).toBe(8);
+  });
+
+  it("says nothing for a header it cannot read", () => {
+    expect(rs("")).toBeNull();
+    expect(rs("default: False")).toBeNull();
+  });
+});
+
+describe("spamReport, precedence and fallback", () => {
+  it("prefers the SpamAssassin set, which is what Stalwart's own filter writes", () => {
+    const r = spamReport({
+      "header:X-Spam-Status:asText": "Yes, score=6.7 required=5.0",
+      "header:X-Spamd-Result:asText": "default: False [1.20 / 15.00];",
+    });
+    expect(r!.source).toBe("spamassassin");
+    expect(r!.verdict).toBe("spam");
+  });
+
+  it("falls back to a bare score, with no threshold to read it against", () => {
+    const r = spamReport({ "header:X-Spam-Score:asText": "+4.1" });
+    expect(r!.score).toBe(4.1);
+    expect(r!.threshold).toBeNull();
+    expect(r!.verdict).toBeNull();
+    expect(r!.rules).toEqual([]);
+  });
+
+  it("does not invent a verdict from score against threshold", () => {
+    // Above the threshold, but the filter did not say "Yes" -- so neither do we.
+    const r = sa("score=9.9 required=5.0 tests=[X=9.9]");
+    expect(r!.verdict).toBeNull();
+  });
+});
diff --git a/web/src/lib/spamScore.ts b/web/src/lib/spamScore.ts
new file mode 100644
index 0000000..925e9b1
--- /dev/null
+++ b/web/src/lib/spamScore.ts
@@ -0,0 +1,146 @@
+/**
+ * What the spam filter in front of the mailbox already said, read back off the
+ * message.
+ *
+ * Nothing here scores anything. The server has already done that at delivery
+ * and written its working into headers; this only reads them, which is why it
+ * costs nothing and cannot disagree with the filter that actually made the
+ * decision.
+ *
+ * Two formats cover what sits in front of a Stalwart mailbox in practice: the
+ * SpamAssassin-shaped `X-Spam-*` set, which Stalwart's own filter writes, and
+ * Rspamd's `X-Spamd-Result`. Anything else is left unread rather than guessed
+ * at -- a misparsed score shown confidently is worse than no panel.
+ *
+ * The one editorial decision: **a score is not shown without its threshold
+ * where the header states one.** 6.7 is damning against a threshold of 5 and
+ * unremarkable against 15, so the number alone is not something a reader can
+ * act on. Where no threshold is stated, that is said rather than assumed.
+ */
+
+export interface SpamRule {
+  /** The rule's own name, as the filter wrote it. */
+  name: string;
+  /** What it contributed. Negative moves the message towards clean. */
+  score: number;
+  /** Rspamd's bracketed note, where there is one. */
+  detail?: string;
+}
+
+export interface SpamReport {
+  /**
+   * What the filter concluded, and only where it said so outright. Left `null`
+   * rather than derived from score against threshold: the filter applies
+   * policy we cannot see, and inventing a verdict it did not state would be
+   * putting words in its mouth.
+   */
+  verdict: "spam" | "clean" | null;
+  score: number | null;
+  threshold: number | null;
+  /** Biggest movers first; ties keep the order the filter listed them in. */
+  rules: SpamRule[];
+  source: "spamassassin" | "rspamd";
+}
+
+/** Headers requested for a full message; kept beside the parser that reads them. */
+export const SPAM_HEADER_PROPS = [
+  "header:X-Spam-Status:asText",
+  "header:X-Spam-Score:asText",
+  "header:X-Spamd-Result:asText",
+] as const;
+
+/** Headers arrive folded, so tabs and newlines are whitespace like any other. */
+function flatten(v: string | null | undefined): string {
+  return (v ?? "").replace(/\s+/g, " ").trim();
+}
+
+function num(raw: string | undefined): number | null {
+  if (raw === undefined) return null;
+  const n = Number(raw);
+  return Number.isFinite(n) ? n : null;
+}
+
+/** Biggest absolute contribution first: what moved the message, in order. */
+function byWeight(rules: SpamRule[]): SpamRule[] {
+  return [...rules].sort((a, b) => Math.abs(b.score) - Math.abs(a.score));
+}
+
+/**
+ * `Yes, score=6.7 required=5.0 tests=[BAYES_99=3.5, HTML_MESSAGE=0.001]`
+ * The verdict word is the only part guaranteed to be there.
+ */
+function parseSpamAssassin(raw: string): SpamReport | null {
+  const s = flatten(raw);
+  if (!s) return null;
+  const verdictWord = /^(yes|no)\b/i.exec(s);
+  const score = num(/\bscore=(-?[\d.]+)/i.exec(s)?.[1]);
+  const threshold = num(/\b(?:required|require)=(-?[\d.]+)/i.exec(s)?.[1]);
+  // Nothing usable: not a header we understand, so say so by returning null
+  // rather than rendering an empty panel.
+  if (!verdictWord && score === null) return null;
+  const rules: SpamRule[] = [];
+  const tests = /\btests=\[([^\]]*)\]/i.exec(s)?.[1];
+  if (tests) {
+    for (const part of tests.split(",")) {
+      const m = /^\s*([A-Za-z0-9_.-]+)\s*=\s*(-?[\d.]+)\s*$/.exec(part);
+      const value = num(m?.[2]);
+      if (m?.[1] && value !== null) rules.push({ name: m[1], score: value });
+    }
+  }
+  return {
+    verdict: verdictWord ? (verdictWord[1]!.toLowerCase() === "yes" ? "spam" : "clean") : null,
+    score,
+    threshold,
+    rules: byWeight(rules),
+    source: "spamassassin",
+  };
+}
+
+/**
+ * `default: False [1.20 / 15.00]; MIME_GOOD(-0.10)[text/plain]; DKIM_ALLOW(-0.20)[]`
+ * The action word before the brackets is the verdict; `False` is not spam.
+ */
+function parseRspamd(raw: string): SpamReport | null {
+  const s = flatten(raw);
+  if (!s) return null;
+  const head = /^[^:]*:\s*(\S+)\s*\[\s*(-?[\d.]+)\s*\/\s*(-?[\d.]+)\s*\]/.exec(s);
+  if (!head) return null;
+  const action = head[1]!.toLowerCase();
+  const rules: SpamRule[] = [];
+  // Each rule after the head, `NAME(score)` with an optional bracketed note.
+  for (const m of s.matchAll(/([A-Z][A-Z0-9_]*)\(\s*(-?[\d.]+)\s*\)(?:\[([^\]]*)\])?/g)) {
+    const value = num(m[2]);
+    if (value === null) continue;
+    const detail = m[3]?.trim();
+    rules.push(detail ? { name: m[1]!, score: value, detail } : { name: m[1]!, score: value });
+  }
+  return {
+    // "False" is Rspamd saying the message is not spam; "True", and the named
+    // actions that reject or bin it, are it saying the opposite. Anything else
+    // -- greylisting, for one -- is not a verdict about the message.
+    verdict: action === "false" ? "clean" : action === "true" || action === "reject" || action === "add_header" || action === "rewrite_subject" ? "spam" : null,
+    score: num(head[2]),
+    threshold: num(head[3]),
+    rules: byWeight(rules),
+    source: "rspamd",
+  };
+}
+
+type HeaderBag = Partial<Record<(typeof SPAM_HEADER_PROPS)[number], string | null>>;
+
+/**
+ * Read whichever of the two the message carries, preferring the SpamAssassin
+ * set because it is what Stalwart's own filter writes; a message that has been
+ * through both keeps the nearer verdict.
+ */
+export function spamReport(e: HeaderBag): SpamReport | null {
+  const sa = parseSpamAssassin(e["header:X-Spam-Status:asText"] ?? "");
+  if (sa) return sa;
+  const rspamd = parseRspamd(e["header:X-Spamd-Result:asText"] ?? "");
+  if (rspamd) return rspamd;
+  // Last resort: a bare score with nothing to read it against. Worth showing,
+  // because the alternative is hiding the only thing the filter said.
+  const bare = num(flatten(e["header:X-Spam-Score:asText"]).replace(/^\+/, "") || undefined);
+  if (bare === null) return null;
+  return { verdict: null, score: bare, threshold: null, rules: [], source: "spamassassin" };
+}
diff --git a/web/src/store/mail.ts b/web/src/store/mail.ts
index 49c9680..d74ab14 100644
--- a/web/src/store/mail.ts
+++ b/web/src/store/mail.ts
@@ -1,5 +1,6 @@
 import { create } from "zustand";
 import type { FolderRef } from "@/lib/sieveFolders";
+import { SPAM_HEADER_PROPS } from "@/lib/spamScore";
 import { groupByArchivePath, archivePath, type ArchiveGranularity } from "@/lib/archiveDate";
 import { JmapMethodError, chunk, client, setErrorMessage } from "@/jmap/client";
 import type {
@@ -90,6 +91,7 @@ export const FULL_PROPS = [
   "header:Auto-Submitted:asText",
   "header:Precedence:asText",
   "header:Authentication-Results:asText",
+  ...SPAM_HEADER_PROPS,
 ];
 
 export const BODY_PROPS = ["partId", "blobId", "size", "name", "type", "charset", "disposition", "cid", "language", "location", "subParts", "headers"];
diff --git a/web/src/styles/app.css b/web/src/styles/app.css
index 1d3509b..3100b0d 100644
--- a/web/src/styles/app.css
+++ b/web/src/styles/app.css
@@ -1377,6 +1377,16 @@ button.dp-open:disabled { cursor: default; opacity: .5; }
 .composer-field label .link-btn:hover { color: var(--accent); }
 .composer-field label .link-btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 3px; }
 
+/* The spam filter's own working, in the message details. */
+.spam-summary { display: flex; flex-direction: column; gap: 6px; }
+/* Capped, so a rule with no note does not fling its score to the far side of a
+   wide reading pane. */
+.spam-rules { list-style: none; margin: 0; padding: 0; display: flex; flex-direction: column; gap: 2px; max-width: 30rem; }
+.spam-rules li { display: grid; grid-template-columns: auto 1fr auto; gap: 8px; align-items: baseline; }
+.spam-weight { font-family: var(--font-mono); font-size: 12px; text-align: right; color: var(--fg-muted); }
+.spam-weight.bad { color: var(--danger); }
+.spam-weight.good { color: var(--success); }
+
 /* The placeholder reference under a template's body. */
 .placeholder-list { display: grid; grid-template-columns: auto 1fr; gap: 4px 12px; align-items: baseline; }
 .placeholder-row { display: contents; }
diff --git a/web/src/views/mail/MessageView.tsx b/web/src/views/mail/MessageView.tsx
index d269827..6b4421a 100644
--- a/web/src/views/mail/MessageView.tsx
+++ b/web/src/views/mail/MessageView.tsx
@@ -10,6 +10,7 @@ import { useContacts } from "@/store/contacts";
 import { useCalendar } from "@/store/calendar";
 import { startAppointment } from "@/lib/appointment";
 import { client } from "@/jmap/client";
+import { spamReport, type SpamReport } from "@/lib/spamScore";
 import { formatFullDate, formatListDate, formatSize } from "@/lib/format";
 import { displayName, formatAddress } from "@/lib/address";
 import { EMAIL_BASE_CSS, TEXT_EMAIL_CSS, htmlDeclaresColors, sanitizeEmailHtml } from "@/lib/html";
@@ -112,6 +113,7 @@ export const MessageView = memo(function MessageView({ email: e, expanded, wasUn
   const isHighPriority = /^[12]/.test(e["header:X-Priority:asText"] ?? "") || /high/i.test(e["header:Importance:asText"] ?? "");
   const receiptRequested = Boolean(e["header:Disposition-Notification-To:asAddresses"]?.length);
   const authFailed = /\b(dkim|spf|dmarc)=fail\b/i.test(e["header:Authentication-Results:asText"] ?? "");
+  const spam = useMemo(() => spamReport(e), [e]);
 
   const openSource = async () => {
     setShowSource(true);
@@ -265,6 +267,7 @@ export const MessageView = memo(function MessageView({ email: e, expanded, wasUn
               {e.messageId?.[0] && <><dt>{translate("Message-ID")}</dt><dd className="mono small">{e.messageId[0]}</dd></>}
               {e["header:List-Id:asText"] && <><dt>{translate("List")}</dt><dd>{e["header:List-Id:asText"]}</dd></>}
               <dt>{translate("Size")}</dt><dd>{formatSize(e.size)}</dd>
+              {spam && <><dt>{translate("Spam filter")}</dt><dd><SpamSummary report={spam} /></dd></>}
               {receiptRequested && <><dt>{translate("Receipt")}</dt><dd>{receipt.offer ? `Requested, to ${receipt.to!.email}. Never sent automatically.` : refusalText(receipt.refusal!)}</dd></>}
             </dl>
           )}
@@ -552,6 +555,53 @@ function TextBody({ text }: { text: string }) {
   );
 }
 
+/* ---------- Spam ---------- */
+
+/**
+ * What the filter said, not what we think of it. The verdict line only claims
+ * as much as the header did: where the filter stated one, it is shown; where
+ * it only left a score, the score is shown on its own rather than being turned
+ * into a verdict here.
+ *
+ * A score is always given its threshold where the header carried one, because
+ * the number is unreadable without it -- 6.7 is damning against 5 and
+ * unremarkable against 15. Where none was stated, that is said.
+ */
+function SpamSummary({ report }: { report: SpamReport }) {
+  const { verdict, score, threshold, rules } = report;
+  return (
+    <div className="spam-summary">
+      <div>
+        {verdict === "spam" && <strong>{translate("Marked as spam")}</strong>}
+        {verdict === "clean" && <strong>{translate("Not spam")}</strong>}
+        {verdict === null && <strong>{translate("No verdict recorded")}</strong>}
+        {score !== null && (
+          <span className="hint">
+            {" — "}
+            {threshold !== null
+              ? translate("scored {score} against a threshold of {threshold}", { score: String(score), threshold: String(threshold) })
+              : translate("scored {score}, with no threshold stated", { score: String(score) })}
+          </span>
+        )}
+      </div>
+      {rules.length > 0 && (
+        <ul className="spam-rules">
+          {rules.map((r, i) => (
+            <li key={`${r.name}-${i}`}>
+              <span className="mono small">{r.name}</span>
+              {r.detail && <span className="hint truncate">{r.detail}</span>}
+              {/* Signed, because which way a rule pushed is the whole point. */}
+              <span className={`spam-weight ${r.score > 0 ? "bad" : r.score < 0 ? "good" : ""}`}>
+                {r.score > 0 ? `+${r.score}` : String(r.score)}
+              </span>
+            </li>
+          ))}
+        </ul>
+      )}
+    </div>
+  );
+}
+
 /* ---------- Attachments ---------- */
 
 export function attachmentIcon(type: string, name?: string | null) {