From 2f9907f24755b59ceb9ae075e26b1e4f606adeec Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Wed, 24 Nov 2021 10:53:49 +0100
Subject: mail: add a custom email policy

Uses structured parsing for more headers.
---
 alot/db/message.py  |  8 ++++----
 alot/mail/policy.py | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 4 deletions(-)
 create mode 100644 alot/mail/policy.py

diff --git a/alot/db/message.py b/alot/db/message.py
index 19a0f043..97ab991f 100644
--- a/alot/db/message.py
+++ b/alot/db/message.py
@@ -5,7 +5,6 @@
 import codecs
 import email
 import email.charset as charset
-import email.policy
 from functools import cached_property
 import logging
 import os
@@ -16,6 +15,7 @@ from datetime import datetime
 from urwid.util import detected_encoding
 
 from ..mail.attachment import Attachment
+from ..mail.policy     import p as policy
 from .. import crypto
 from .. import helper
 from ..errors import GPGProblem
@@ -384,7 +384,7 @@ class _MimeTree:
             d    = None
 
         if d:
-            child = email.message_from_bytes(d, policy = email.policy.SMTP)
+            child = email.message_from_bytes(d, policy = policy)
             self.children = [_MimeTree(child, session_keys)]
 
         if sigs:
@@ -503,11 +503,11 @@ class Message:
     def _email(self):
         try:
             with open(self.filename, 'rb') as f:
-                mail = email.message_from_bytes(f.read(), policy = email.policy.SMTP)
+                mail = email.message_from_bytes(f.read(), policy = policy)
         except IOError:
             warning = b"Subject: Caution!\n"\
                       b"Message file is no longer accessible:\n%s" % self.filename
-            mail = email.message_from_bytes(warning, policy = email.policy.SMTP)
+            mail = email.message_from_bytes(warning, policy = policy)
 
         return mail
 
diff --git a/alot/mail/policy.py b/alot/mail/policy.py
new file mode 100644
index 00000000..1b9f07c3
--- /dev/null
+++ b/alot/mail/policy.py
@@ -0,0 +1,19 @@
+# This file is released under the GNU GPL, version 3 or a later revision.
+# For further details see the COPYING file
+
+import email.policy         as _p
+import email.headerregistry as _hdr
+
+from . import headers as HDR
+
+_headers = {
+    HDR.X_BEEN_THERE   : _hdr.UniqueAddressHeader,
+    HDR.X_MAILING_LIST : _hdr.UniqueAddressHeader,
+}
+
+# here we define our custom policy that handles additional headers
+# derive from SMTP
+p = _p.EmailPolicy() + _p.SMTP
+
+for h, t in _headers.items():
+    p.header_factory.map_to_type(h, t)
-- 
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