From 786adfd3417136c78529f81775fe38eda9ae9e7d Mon Sep 17 00:00:00 2001
From: s-aga-r <sagarsharma.s312@gmail.com>
Date: Mon, 9 Feb 2026 10:42:19 +0530
Subject: [PATCH] fix(Communication): set `In-Reply-To` (#36746)

---
 frappe/core/doctype/communication/email.py      | 5 +++++
 frappe/core/doctype/communication/mixins.py     | 1 +
 frappe/email/doctype/email_queue/email_queue.py | 3 ++-
 frappe/public/js/frappe/views/communication.js  | 1 +
 4 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/frappe/core/doctype/communication/email.py b/frappe/core/doctype/communication/email.py
index acbc27b2be..a3929a5860 100755
--- a/frappe/core/doctype/communication/email.py
+++ b/frappe/core/doctype/communication/email.py
@@ -52,6 +52,7 @@ def make(
 	now=False,
 	raw_html=False,
 	add_css=True,
+	in_reply_to=None,
 	**kwargs,
 ) -> dict[str, str]:
 	"""Make a new communication. Checks for email permissions for specified Document.
@@ -73,6 +74,7 @@ def make(
 	:param send_after: Send after the given datetime.
 	:param raw_html: Whether to use html version of email template
 	:param add_css: Add default CSS from hooks/email_css to the email template (default **True**)
+	:param in_reply_to: Name of the Communication document to which this communication is a reply.
 	"""
 	from frappe.utils.commands import warn
 
@@ -127,6 +129,7 @@ def make(
 		now=now,
 		raw_html=raw_html,
 		add_css=add_css,
+		in_reply_to=in_reply_to,
 	)
 
 
@@ -157,6 +160,7 @@ def _make(
 	now=False,
 	raw_html=False,
 	add_css=True,
+	in_reply_to=None,
 ) -> dict[str, str]:
 	"""Internal method to make a new communication that ignores Permission checks."""
 
@@ -185,6 +189,7 @@ def _make(
 			"has_attachment": 1 if attachments else 0,
 			"communication_type": communication_type,
 			"send_after": send_after,
+			"in_reply_to": in_reply_to,
 		}
 	)
 	comm.flags.skip_add_signature = not add_signature or (
diff --git a/frappe/core/doctype/communication/mixins.py b/frappe/core/doctype/communication/mixins.py
index edf14baca5..b2aaeb3979 100644
--- a/frappe/core/doctype/communication/mixins.py
+++ b/frappe/core/doctype/communication/mixins.py
@@ -311,6 +311,7 @@ class CommunicationEmailMixin:
 			"send_after": self.send_after,
 			"raw_html": raw_html,
 			"add_css": add_css,
+			"in_reply_to": self.in_reply_to,
 		}
 
 	def send_email(
diff --git a/frappe/email/doctype/email_queue/email_queue.py b/frappe/email/doctype/email_queue/email_queue.py
index 3ce20a0d12..738125799c 100644
--- a/frappe/email/doctype/email_queue/email_queue.py
+++ b/frappe/email/doctype/email_queue/email_queue.py
@@ -755,7 +755,8 @@ class QueueBuilder:
 			mail.msg_root["Disposition-Notification-To"] = self.sender
 		if self.in_reply_to:
 			if message_id := frappe.db.get_value("Communication", self.in_reply_to, "message_id"):
-				mail.set_in_reply_to(get_string_between("<", message_id, ">"))
+				message_id = message_id.strip("<> \t\n")
+				mail.set_in_reply_to(f"<{message_id}>")
 		return mail
 
 	def process(self, send_now=False) -> EmailQueue | None:
diff --git a/frappe/public/js/frappe/views/communication.js b/frappe/public/js/frappe/views/communication.js
index bd6c0b7865..34871f275b 100755
--- a/frappe/public/js/frappe/views/communication.js
+++ b/frappe/public/js/frappe/views/communication.js
@@ -870,6 +870,7 @@ frappe.views.CommunicationComposer = class {
 				print_language: form_values.print_language,
 				raw_html: form_values.use_html,
 				add_css: form_values.add_css,
+				in_reply_to: (this.is_a_reply && this.last_email?.name) || null,
 			},
 			btn,
 			callback(r) {