Email: always use quoted-printable (#6617)

src/pretix/base/services/mail.py

@@ -54,7 +54,7 @@ from celery.exceptions import MaxRetriesExceededError
 from django.conf import settings
 from django.core.files.storage import default_storage
 from django.core.mail import EmailMultiAlternatives, SafeMIMEMultipart
-from django.core.mail.message import SafeMIMEText
+from django.core.mail.message import SafeMIMEText, utf8_charset_qp
 from django.db import connection, transaction
 from django.db.models import Q
 from django.dispatch import receiver
@@ -380,6 +380,8 @@ def mail(email: Union[str, Sequence[str]], subject: Union[str, FormattedString],
 
 
 class CustomEmail(EmailMultiAlternatives):
+    encoding = utf8_charset_qp
+
     def _create_mime_attachment(self, content, mimetype):
         """
         Convert the content, mimetype pair into a MIME attachment object.
@@ -449,9 +451,9 @@ def mail_send_task(self, **kwargs) -> bool:
 
     # Rewrite all <img> tags from real URLs or data URLs to inline attachments referred to by content ID
     if outgoing_mail.body_html is not None:
-        html_message = SafeMIMEMultipart(_subtype='related', encoding=settings.DEFAULT_CHARSET)
+        html_message = SafeMIMEMultipart(_subtype='related')
         html_with_cid, cid_images = replace_images_with_cid_paths(outgoing_mail.body_html)
-        html_message.attach(SafeMIMEText(html_with_cid, 'html', settings.DEFAULT_CHARSET))
+        html_message.attach(SafeMIMEText(html_with_cid, 'html', utf8_charset_qp))
         attach_cid_images(html_message, cid_images, verify_ssl=True)
         email.attach_alternative(html_message, "multipart/related")
 

src/tests/base/test_mail.py

@@ -34,6 +34,7 @@
 
 import datetime
 import os
+import quopri
 import re
 import socket
 from contextlib import contextmanager
@@ -316,8 +317,10 @@ def _extract_html(mail):
         if "multipart/related" in mimetype:
             for sp in content._payload:
                 if isinstance(sp, MIMEText):
-                    return sp._payload
-                    break
+                    if sp.get('content-transfer-encoding').startswith('quoted-printable'):
+                        return quopri.decodestring(sp.get_payload()).decode()
+                    else:
+                        return sp.get_payload()
         elif "text/html" in mimetype:
             return content
 
@@ -711,3 +714,29 @@ def test_send_mail_private_ip(res, use_ssl, allow_private_networks, env):
             assert m.status == OutgoingMail.STATUS_SENT
         else:
             assert m.status == OutgoingMail.STATUS_FAILED
+
+
+@pytest.mark.django_db
+def test_mail_encoding(env, mailoutbox):
+    m = OutgoingMail.objects.create(
+        to=['recipient@example.com'],
+        subject='Test',
+        body_plain='Test öäü testtesttest',
+        body_html='Test <b>ÖÄÜ</b>',
+        sender='sender@example.com',
+    )
+    assert m.status == OutgoingMail.STATUS_QUEUED
+    mail_send_task.apply(kwargs={
+        'outgoing_mail': m.pk,
+    }, max_retries=0)
+    m.refresh_from_db()
+    assert m.status == OutgoingMail.STATUS_SENT
+
+    assert len(mailoutbox) == 1
+    mail_plain = mailoutbox[0].message().as_string()
+
+    assert "ä" not in mail_plain
+    assert "Ä" not in mail_plain
+    assert "Test =C3=B6=C3=A4=C3=BC" in mail_plain
+    assert "Test <b>=C3=96=C3=84=C3=9C</b>" in mail_plain
+    assert max(len(x) for x in mail_plain.splitlines()) <= 76