set In-Reply-To header out outgoing email when DestinationReference is set on the document

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@42776 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/EmailDocument.py

@@ -626,6 +626,8 @@ class EmailDocument(TextDocument):
     if not _checkPermission(Permissions.View, self):
       raise Unauthorized
 
+    additional_headers = {}
+
     #
     # Build mail message
     # This part will be replaced with MailTemplate soon.
@@ -652,9 +654,13 @@ class EmailDocument(TextDocument):
     # Return-Path
     if reply_url is None:
       reply_url = self.portal_preferences.getPreferredEventSenderEmail()
-    additional_headers = None
     if reply_url:
-      additional_headers = {'Return-Path':reply_url}
+      additional_headers['Return-Path'] = reply_url
+
+    # Reply-To
+    destination_reference = self.getDestinationReference()
+    if destination_reference is not None:
+      additional_headers['In-Reply-To'] = destination_reference
 
     # To (multiple)
     to_url_list = []