human handoffs

backend/app/services/mail_sender.py

@@ -20,6 +20,9 @@ def build_message(
     body_text: str,
     body_html: str | None,
     reply_to: str | None = None,
+    in_reply_to: str | None = None,
+    references: list[str] | None = None,
+    message_id: str | None = None,
 ) -> EmailMessage:
     message = EmailMessage(policy=SMTP_POLICY)
     message["From"] = sender
@@ -30,7 +33,12 @@ def build_message(
         message["Reply-To"] = reply_to
     message["Subject"] = subject
     message["Date"] = email.utils.formatdate(localtime=True)
-    message["Message-ID"] = email.utils.make_msgid(domain=sender.split("@")[-1])
+    generated_id = message_id or email.utils.make_msgid(domain=sender.split("@")[-1])
+    message["Message-ID"] = generated_id
+    if in_reply_to:
+        message["In-Reply-To"] = in_reply_to
+    if references:
+        message["References"] = " ".join(references)
     message.set_content(body_text)
     if body_html:
         message.add_alternative(body_html, subtype="html")
@@ -95,7 +103,10 @@ async def deliver_email(
     body_html: str | None,
     domain: MailDomain,
     reply_to: str | None = None,
-) -> None:
+    in_reply_to: str | None = None,
+    references: list[str] | None = None,
+    message_id: str | None = None,
+) -> str:
     message = build_message(
         sender=sender,
         recipients=recipients,
@@ -104,6 +115,9 @@ async def deliver_email(
         body_text=body_text,
         body_html=body_html,
         reply_to=reply_to,
+        in_reply_to=in_reply_to,
+        references=references,
+        message_id=message_id,
     )
     signed = sign_message(message, domain)
     await send_via_smtp(
@@ -111,3 +125,4 @@ async def deliver_email(
         sender=sender,
         recipients=[*recipients, *cc, *bcc],
     )
+    return str(message["Message-ID"])