diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3a769c0..a84f79e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## 0.1.16
+
+- Include the selected message as quoted HTML and plain text in replies so email clients can
+  collapse and expand the previous content.
+
 ## 0.1.15
 
 - Send new messages, replies, and forwards with Command+Enter on macOS or Control+Enter elsewhere.
diff --git a/package.json b/package.json
index 57b3b81..62eaa45 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "hqbase",
-  "version": "0.1.15",
+  "version": "0.1.16",
   "private": true,
   "type": "module",
   "packageManager": "pnpm@11.7.0",
diff --git a/test/unit/worker/features/send/reply-body.test.ts b/test/unit/worker/features/send/reply-body.test.ts
new file mode 100644
index 0000000..13c4e86
--- /dev/null
+++ b/test/unit/worker/features/send/reply-body.test.ts
@@ -0,0 +1,39 @@
+import { buildReplyBody } from "@worker/features/send/reply-body";
+import { describe, expect, it } from "vitest";
+
+const original = {
+  createdAt: "2026-07-28T15:30:00.000Z",
+  fromAddress: "owner@example.com",
+  receivedAt: "2026-07-28T15:29:00.000Z",
+  sentAt: null,
+  snippet: "Fallback",
+  textBody: "First line\r\n\r\nSecond <line> & more"
+};
+
+describe("reply body", () => {
+  it("appends conventional plain-text and Gmail-compatible HTML quotes", () => {
+    const body = buildReplyBody({ html: "<p>Thanks</p>", text: "Thanks" }, original);
+
+    expect(body.text).toBe(
+      [
+        "Thanks",
+        "",
+        "On 2026-07-28 at 15:29 UTC, owner@example.com wrote:",
+        "> First line",
+        ">",
+        "> Second <line> & more"
+      ].join("\n")
+    );
+    expect(body.html).toContain('class="gmail_quote gmail_quote_container"');
+    expect(body.html).toContain('class="gmail_attr"');
+    expect(body.html).toContain("Second &lt;line&gt; &amp; more");
+    expect(body.html).not.toContain("Second <line>");
+  });
+
+  it("bounds quoted message content", () => {
+    const body = buildReplyBody({ text: "Reply" }, { ...original, textBody: "a".repeat(100_001) });
+
+    expect(body.text).toContain("[Previous message truncated by HQBase]");
+    expect(body.html).toBeUndefined();
+  });
+});
diff --git a/test/unit/worker/features/send/send-service.test.ts b/test/unit/worker/features/send/send-service.test.ts
index 422cddb..af5e41f 100644
--- a/test/unit/worker/features/send/send-service.test.ts
+++ b/test/unit/worker/features/send/send-service.test.ts
@@ -124,11 +124,15 @@ describe("send service", () => {
       bcc: ["audit@example.com"],
       cc: ["manager@example.com"],
       from: mailbox.address,
+      html: "<p>Reply</p>",
       messageId: "message-1",
       text: "Reply",
       to: ["alternate@example.com"]
     });
 
+    const quotedText = "Reply\n\nOn 2026-07-10 at 00:00 UTC, owner@example.com wrote:\n> Original";
+    const quotedHtml =
+      '<p>Reply</p><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr"><br>On 2026-07-10 at 00:00 UTC, owner@example.com wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Original</blockquote></div>';
     expect(send).toHaveBeenCalledWith({
       from: mailbox.address,
       bcc: ["audit@example.com"],
@@ -137,8 +141,9 @@ describe("send service", () => {
         "In-Reply-To": "<original@example.com>",
         References: "<earlier@example.com> <original@example.com>"
       },
+      html: quotedHtml,
       subject: "Re: Hello",
-      text: "Reply",
+      text: quotedText,
       to: ["alternate@example.com"]
     });
     expect(insertMessage).toHaveBeenCalledWith(
@@ -146,9 +151,14 @@ describe("send service", () => {
       expect.objectContaining({
         bcc: ["audit@example.com"],
         cc: ["manager@example.com"],
+        htmlR2Key: "sent/2026-07-10/html-1.html",
         messageId: "<cloudflare-reply@example.com>",
+        textBody: quotedText,
         to: ["alternate@example.com"]
       })
     );
+    expect(put).toHaveBeenCalledWith("sent/2026-07-10/html-1.html", quotedHtml, {
+      httpMetadata: { contentType: "text/html; charset=utf-8" }
+    });
   });
 });
diff --git a/worker/features/send/reply-body.ts b/worker/features/send/reply-body.ts
new file mode 100644
index 0000000..c7df2cd
--- /dev/null
+++ b/worker/features/send/reply-body.ts
@@ -0,0 +1,68 @@
+import type { MessageDetail } from "../messages/types";
+
+const maxQuotedCharacters = 100_000;
+const truncationNotice = "[Previous message truncated by HQBase]";
+
+type ReplySource = Pick<
+  MessageDetail,
+  "createdAt" | "fromAddress" | "receivedAt" | "sentAt" | "snippet" | "textBody"
+>;
+
+export function buildReplyBody(
+  authored: { html?: string | undefined; text: string },
+  original: ReplySource
+): { html?: string | undefined; text: string } {
+  const attribution = `On ${formatTimestamp(
+    original.receivedAt ?? original.sentAt ?? original.createdAt
+  )}, ${original.fromAddress} wrote:`;
+  const quoted = boundedQuoteSource(original.textBody || original.snippet);
+  const text = `${authored.text.trimEnd()}\n\n${attribution}\n${quotePlainText(quoted)}`;
+
+  if (!authored.html) return { text };
+
+  return {
+    text,
+    html: `${authored.html.trimEnd()}${quoteHtml(attribution, quoted)}`
+  };
+}
+
+function boundedQuoteSource(value: string): string {
+  const normalized = value.replace(/\r\n?/g, "\n").trim();
+  if (normalized.length <= maxQuotedCharacters) return normalized;
+  return `${normalized.slice(0, maxQuotedCharacters).trimEnd()}\n\n${truncationNotice}`;
+}
+
+function quotePlainText(value: string): string {
+  return value
+    .split("\n")
+    .map((line) => (line ? `> ${line}` : ">"))
+    .join("\n");
+}
+
+function quoteHtml(attribution: string, value: string): string {
+  const quotedHtml = escapeHtml(value).replaceAll("\n", "<br>");
+  return [
+    '<div class="gmail_quote gmail_quote_container">',
+    `<div dir="ltr" class="gmail_attr"><br>${escapeHtml(attribution)}<br></div>`,
+    '<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">',
+    quotedHtml,
+    "</blockquote>",
+    "</div>"
+  ].join("");
+}
+
+function formatTimestamp(value: string): string {
+  const date = new Date(value);
+  if (Number.isNaN(date.getTime())) return value;
+  const [day, time = ""] = date.toISOString().split("T");
+  return `${day} at ${time.slice(0, 5)} UTC`;
+}
+
+function escapeHtml(value: string): string {
+  return value
+    .replaceAll("&", "&amp;")
+    .replaceAll("<", "&lt;")
+    .replaceAll(">", "&gt;")
+    .replaceAll('"', "&quot;")
+    .replaceAll("'", "&#039;");
+}
diff --git a/worker/features/send/service.ts b/worker/features/send/service.ts
index 2687569..b97e9c2 100644
--- a/worker/features/send/service.ts
+++ b/worker/features/send/service.ts
@@ -13,6 +13,7 @@ import {
 } from "../messages/queries";
 import type { MessageSummary } from "../messages/types";
 
+import { buildReplyBody } from "./reply-body";
 import type { ReplyMessageInput, SendMessageInput } from "./validation";
 
 export async function sendNewMessage(
@@ -68,6 +69,7 @@ export async function replyToMessage(
     (value): value is string => value !== null
   );
   const to = input.to?.length ? input.to : [original.fromAddress];
+  const body = buildReplyBody(input, original);
 
   const attachments = await loadAttachments(env, input.attachmentIds, userId);
   const sendResult = await env.MAIL_SENDER.send({
@@ -76,12 +78,12 @@ export async function replyToMessage(
     ...(input.cc.length ? { cc: input.cc } : {}),
     ...(input.bcc.length ? { bcc: input.bcc } : {}),
     subject: ensureReplySubject(original.subject),
-    text: input.text,
+    text: body.text,
     headers: {
       "In-Reply-To": original.messageId ?? original.id,
       References: references.join(" ")
     },
-    ...(input.html ? { html: input.html } : {}),
+    ...(body.html ? { html: body.html } : {}),
     ...(attachments.length ? { attachments: attachments.map(asEmailAttachment) } : {})
   });
 
@@ -91,8 +93,8 @@ export async function replyToMessage(
     cc: input.cc,
     bcc: input.bcc,
     subject: ensureReplySubject(original.subject),
-    text: input.text,
-    ...(input.html ? { html: input.html } : {}),
+    text: body.text,
+    ...(body.html ? { html: body.html } : {}),
     inReplyTo: original.messageId ?? original.id,
     messageId: sendResult.messageId,
     references,