diff --git a/nginx.example.conf b/nginx.example.conf
index 79984c0..0bccab7 100644
--- a/nginx.example.conf
+++ b/nginx.example.conf
@@ -6,17 +6,22 @@ server {
 
     client_max_body_size 60m;
 
-    # ihasmail serves its bundle uncompressed and leaves this to the proxy, so
-    # without these directives the browser downloads about 915 KB where 307 KB
-    # would do. text/event-stream is deliberately absent from gzip_types: the
-    # push stream must not be compressed or buffered.
+    # Compression. The bundle is the bulk of first load -- about 933 KB
+    # uncompressed against 311 KB gzipped -- and nginx passes through anything
+    # the upstream already encoded rather than re-encoding it, so this is
+    # correct whether or not ihasmail compresses on its own.
+    #
+    # text/event-stream is deliberately absent from gzip_types: the push stream
+    # must not be compressed or buffered, which is also why proxy_buffering is
+    # off below.
     gzip on;
     gzip_vary on;
     gzip_proxied any;
     gzip_comp_level 5;
     gzip_min_length 1024;
-    # ihasmail serves scripts as text/javascript, so listing only
-    # application/javascript silently leaves the largest asset uncompressed.
+    # text/javascript is listed explicitly: ihasmail serves scripts with that
+    # type rather than application/javascript, so a conventional gzip_types
+    # list compresses the stylesheet and leaves the largest asset alone.
     gzip_types
         application/javascript
         application/json
diff --git a/server/src/app.ts b/server/src/app.ts
index ed0156e..f543a20 100644
--- a/server/src/app.ts
+++ b/server/src/app.ts
@@ -1,6 +1,7 @@
 import { Hono } from "hono";
 import type { Context, MiddlewareHandler } from "hono";
 import { getCookie, setCookie, deleteCookie } from "hono/cookie";
+import { compress } from "hono/compress";
 import { getConnInfo } from "@hono/node-server/conninfo";
 import { config } from "./config.js";
 import { SessionStore, type SessionBackend, type LiveSession } from "./sessions.js";
@@ -109,6 +110,62 @@ const securityHeaders: MiddlewareHandler = async (c, next) => {
 };
 
 /** CSRF: require our custom header on all API calls; reject cross-site fetches. */
+/**
+ * Routes that forward somebody else's bytes rather than producing our own.
+ *
+ * Compression is right for the app shell, the bundle and our JSON; it is not
+ * worth the risk on the proxy paths. Those carry a content-length copied from
+ * upstream under the rules in `forwardedContentLength`, and issue #76 was a
+ * silent truncation caused by exactly that header disagreeing with the body.
+ * Re-encoding them would be safe in principle -- the length is dropped and the
+ * response goes out chunked -- but the payloads are attachments, images and
+ * calendar data that are already compressed or too small to matter, so there
+ * is nothing to win and a scar to respect.
+ *
+ * `/api/events` needs no entry here: Hono skips `text/event-stream` by content
+ * type. It is listed anyway, because a future change to that route's type
+ * should not quietly start buffering the push stream.
+ */
+const UNCOMPRESSED_ROUTES = [
+  "/api/blob/",
+  "/api/image",
+  "/api/ics",
+  "/api/upload/",
+  "/api/events",
+  /*
+   * The liveness probe, which is small enough that gzip makes it bigger: 53
+   * bytes becomes 73. Hono's size threshold cannot catch this on its own,
+   * because it only applies when the response carries a content-length and
+   * `c.json()` does not set one. Every other JSON route is left compressed --
+   * a JMAP response can run to hundreds of kilobytes and its length is just as
+   * unknown -- so this is the one place worth naming.
+   */
+  "/api/health",
+];
+
+/**
+ * gzip for what we generate.
+ *
+ * The bundle ships uncompressed otherwise: 915 KB on the wire where 307 KB
+ * would do, on every first load. `Caddyfile.example` and
+ * `nginx.example.conf` both compress at the proxy, but that only helps the
+ * deployments that use them, and the default should not depend on reading the
+ * examples.
+ *
+ * Hono's middleware declines anything already carrying `Content-Encoding` or
+ * `Transfer-Encoding`, so a proxy compressing in front of us wins and we do
+ * not double-encode.
+ */
+function compressResponses(basePath: string): MiddlewareHandler {
+  const inner = compress({ threshold: 1024 });
+  const skip = UNCOMPRESSED_ROUTES.map((r) => `${basePath}${r}`);
+  return async (c, next) => {
+    const path = new URL(c.req.url).pathname;
+    if (skip.some((prefix) => path.startsWith(prefix))) return next();
+    return inner(c, next);
+  };
+}
+
 const csrfGuard: MiddlewareHandler = async (c, next) => {
   const site = c.req.header("sec-fetch-site");
   if (site && site !== "same-origin" && site !== "none") {
@@ -178,6 +235,7 @@ function upstreamFailure(c: Context, err: unknown) {
 export function createApp(basePath = config.basePath): Hono<Env> {
   const app = new Hono<Env>();
   app.use("*", securityHeaders);
+  app.use("*", compressResponses(basePath));
 
   const api = new Hono<Env>();
   api.use("*", csrfGuard);
diff --git a/server/src/compress.test.ts b/server/src/compress.test.ts
new file mode 100644
index 0000000..49da5e6
--- /dev/null
+++ b/server/src/compress.test.ts
@@ -0,0 +1,76 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { mkdtempSync, writeFileSync, mkdirSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+/*
+ * A static root of our own, built before the app is imported.
+ *
+ * CI runs `npm test` before `npm run build`, so `web/dist` does not exist when
+ * these run: pointing at it would serve the "web build not found" fallback,
+ * which is short, plain text and rightly uncompressed. That failure looked
+ * exactly like compression being broken.
+ */
+const root = mkdtempSync(join(tmpdir(), "ihasmail-compress-"));
+mkdirSync(join(root, "assets"));
+const script = `/* ${"x".repeat(40_000)} */\n`;
+writeFileSync(join(root, "assets", "app.js"), script);
+writeFileSync(join(root, "index.html"), `<!doctype html><title>t</title>${"<p>hello</p>".repeat(400)}`);
+
+process.env.STATIC_DIR = root;
+process.env.STALWART_URL = "http://127.0.0.1:1";
+const { createApp } = await import("./app.js");
+
+test("an asset is gzipped when the client asks for it", async () => {
+  const res = await createApp().request("/assets/app.js", { headers: { "accept-encoding": "gzip" } });
+  assert.equal(res.status, 200);
+  assert.equal(res.headers.get("content-encoding"), "gzip");
+  assert.match(res.headers.get("vary") ?? "", /accept-encoding/i);
+});
+
+test("a client that does not ask for gzip does not get it", async () => {
+  const res = await createApp().request("/assets/app.js", { headers: { "accept-encoding": "identity" } });
+  assert.equal(res.status, 200);
+  assert.equal(res.headers.get("content-encoding"), null);
+});
+
+test("gzip actually makes the asset smaller", async () => {
+  const plain = await (await createApp().request("/assets/app.js", { headers: { "accept-encoding": "identity" } })).arrayBuffer();
+  const gz = await (await createApp().request("/assets/app.js", { headers: { "accept-encoding": "gzip" } })).arrayBuffer();
+  assert.ok(gz.byteLength < plain.byteLength / 2, `${gz.byteLength} should be well under ${plain.byteLength}`);
+});
+
+test("a gzipped response decodes to the bytes we would have sent plain", async () => {
+  const plain = await (await createApp().request("/assets/app.js", { headers: { "accept-encoding": "identity" } })).arrayBuffer();
+  const res = await createApp().request("/assets/app.js", { headers: { "accept-encoding": "gzip" } });
+  const decoded = await new Response(res.body!.pipeThrough(new DecompressionStream("gzip"))).arrayBuffer();
+  assert.deepEqual(Buffer.from(decoded), Buffer.from(plain));
+});
+
+test("the app shell is gzipped", async () => {
+  const res = await createApp().request("/", { headers: { "accept-encoding": "gzip" } });
+  assert.equal(res.status, 200);
+  assert.equal(res.headers.get("content-encoding"), "gzip");
+});
+
+test("proxy routes that forward upstream bytes are never compressed", async () => {
+  // Unauthenticated, so these stop at 401 -- enough to prove the middleware
+  // declines the path, which is what issue #76 was about.
+  const app = createApp();
+  for (const path of ["/api/blob/a/b/c.pdf", "/api/image?url=https://example.com/x.png", "/api/ics?url=https://example.com/x.ics"]) {
+    const res = await app.request(path, { headers: { "accept-encoding": "gzip" } });
+    assert.equal(res.headers.get("content-encoding"), null, `${path} must not be compressed`);
+  }
+});
+
+test("the push stream is never compressed", async () => {
+  const res = await createApp().request("/api/events", { headers: { "accept-encoding": "gzip" } });
+  assert.equal(res.headers.get("content-encoding"), null);
+});
+
+test("the liveness probe is not compressed, since gzip would make it bigger", async () => {
+  const res = await createApp().request("/api/health", { headers: { "accept-encoding": "gzip" } });
+  assert.equal(res.status, 200);
+  assert.equal(res.headers.get("content-encoding"), null);
+});