diff --git a/README.md b/README.md
index faa34a7..0d97a21 100644
--- a/README.md
+++ b/README.md
@@ -158,7 +158,7 @@ Emails are sent only from drafts. Create or edit a draft with `save_draft`/`edit
 
 ### Replying to an email
 
-Use `in_reply_to_email_id` on `save_draft` or `edit_draft` to create a reply without a separate tool. Then send it with `send_draft`.
+Use `in_reply_to_email_id` on `save_draft` or `edit_draft` to create a reply without a separate tool. The draft includes reply headers and a quoted original message so webmail clients can preserve threading on send. Then send it with `send_draft`.
 
 - Provide `in_reply_to_email_id` (and optionally `in_reply_to_mailbox`, default `INBOX`).
 - `reply_all=true` includes original recipients; otherwise it replies to the sender/Reply-To.
diff --git a/src/services/email_service.py b/src/services/email_service.py
index 7bf9cd2..f7d2ae0 100644
--- a/src/services/email_service.py
+++ b/src/services/email_service.py
@@ -1,4 +1,5 @@
 import email
+import html
 from email.header import decode_header
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
@@ -464,9 +465,11 @@ class EmailService:
                     cc = context["cc"]
                 in_reply_to = context["in_reply_to"]
                 references = context["references"]
+                original = context["original"]
             else:
                 in_reply_to = None
                 references = None
+                original = None
 
             if not to:
                 return OperationResult(success=False, message="'to' is required for drafts")
@@ -475,6 +478,9 @@ class EmailService:
             if body is None:
                 return OperationResult(success=False, message="'body' is required for drafts")
 
+            if original:
+                body, html_body = self._build_reply_bodies(original, body)
+
             msg = self._build_draft_message(
                 to=to,
                 subject=subject,
@@ -554,9 +560,11 @@ class EmailService:
                 resolved_cc = context["cc"]
             in_reply_to = context["in_reply_to"]
             references = context["references"]
+            original = context["original"]
         else:
             in_reply_to = None
             references = None
+            original = None
 
         try:
             client = self._get_imap_client()
@@ -565,6 +573,9 @@ class EmailService:
             client.delete_messages([uid])
             client.expunge()
 
+            if original:
+                resolved_body, resolved_html = self._build_reply_bodies(original, resolved_body)
+
             msg = self._build_draft_message(
                 to=resolved_to,
                 subject=resolved_subject,
@@ -975,6 +986,7 @@ class EmailService:
             references.append(in_reply_to)
 
         return {
+            "original": original,
             "to": to,
             "cc": reply_cc or None,
             "subject": subject,
@@ -982,6 +994,44 @@ class EmailService:
             "references": references or None,
         }, None
 
+    def _build_reply_bodies(self, original: Email, body_text: str) -> tuple[str, Optional[str]]:
+        intro = self._format_reply_intro(original)
+        quoted_text = original.body_text or ""
+        text = body_text or ""
+        if intro:
+            text = f"{text}\n\n{intro}\n\n{quoted_text}".rstrip()
+
+        html_body = None
+        quoted_html = original.body_html
+        if not quoted_html and quoted_text:
+            quoted_html = html.escape(quoted_text).replace("\n", "<br/>")
+        if quoted_html:
+            cite = original.headers.get("Message-ID") or original.in_reply_to or ""
+            cite_attr = f' cite="{html.escape(cite)}"' if cite else ""
+            html_intro = html.escape(intro).replace("\n", "<br/>")
+            html_body = (
+                f"<div>{html.escape(body_text).replace('\\n', '<br/>')}</div>"
+                f"<br/><br/>{html_intro}<br/><br/>"
+                f"<blockquote type=\"cite\"{cite_attr}>"
+                f"<div dir=\"ltr\">{quoted_html}</div>"
+                f"</blockquote><br/><br/><br/>"
+            )
+
+        return text, html_body
+
+    def _format_reply_intro(self, original: Email) -> str:
+        date_str = ""
+        if original.date:
+            try:
+                date_str = original.date.strftime("%A, %B %d, %Y %H:%M %Z").strip()
+            except Exception:
+                date_str = str(original.date)
+        from_name = original.from_address.name or original.from_address.email
+        from_email = original.from_address.email
+        if date_str:
+            return f"On {date_str}, {from_name} <{from_email}> wrote:"
+        return f"On {from_name} <{from_email}> wrote:"
+
     def _resolve_sender(
         self, sender_email: Optional[str], sender_name: Optional[str]
     ) -> tuple[Optional[str], str]: