Emails with attachments cause server error in Django 5.2

[kevinrenskers]

I am sending a EmailMultiAlternatives with an attachment, and this causes a server error in Django 5.2.

Code:

from django.conf import settings
from django.core.mail import EmailMultiAlternatives
from django.db import models
from django.template.loader import render_to_string
from weasyprint import HTML


class Order(models.Model):
    # fields...

    def send_order_placed_email(self):
        text_body = render_to_string("shop/orders/order_placed_email.txt", {"order": self, "settings": settings})
        html_body = render_to_string("shop/orders/order_placed_email.html", {"order": self, "settings": settings})

        invoice_html = render_to_string("shop/orders/invoice.html", {"order": self, "settings": settings})
        invoice_pdf = HTML(string=invoice_html).write_pdf(cache=pdf_cache)

        message = EmailMultiAlternatives(
            subject="Thank you for your purchase!",
            body=text_body,
            to=[self.email],
        )
        message.attach_alternative(html_body, "text/html")
        message.attach("invoice.pdf", invoice_pdf, "application/pdf")
        message.send()

Error:

>>> order = Order.objects.get(id=42679955)
>>> order.send_order_placed_email()
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/Users/kevin/Workspace/api.example.com/shop/orders/models.py", line 247, in send_order_placed_email
    message.send()
    ~~~~~~~~~~~~^^
  File "/Users/kevin/Workspace/api.example.com/.venv/lib/python3.13/site-packages/django/core/mail/message.py", line 307, in send
    return self.get_connection(fail_silently).send_messages([self])
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^
  File "/Users/kevin/Workspace/api.example.com/.venv/lib/python3.13/site-packages/mailer/backend.py", line 12, in send_messages
    messages = Message.objects.bulk_create([Message(email=email) for email in email_messages], MESSAGES_BATCH_SIZE)
                                            ~~~~~~~^^^^^^^^^^^^^
  File "/Users/kevin/Workspace/api.example.com/.venv/lib/python3.13/site-packages/django/db/models/base.py", line 558, in __init__
    _setattr(self, prop, value)
    ~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/Users/kevin/Workspace/api.example.com/.venv/lib/python3.13/site-packages/mailer/models.py", line 148, in _set_email
    self.message_data = email_to_db(val)
                        ~~~~~~~~~~~^^^^^
  File "/Users/kevin/Workspace/api.example.com/.venv/lib/python3.13/site-packages/mailer/models.py", line 94, in email_to_db
    return base64_encode(pickle.dumps(email)).decode("ascii")
                         ~~~~~~~~~~~~^^^^^^^
_pickle.PicklingError: Can't pickle <class 'django.core.mail.message.Attachment'>: attribute lookup Attachment on django.core.mail.message failed

[almiavicas]

Just found the same issue in Django 5.2, python 3.12. Here is my code:

from typing import List
import traceback
from django.core.validators import validate_email
from django.core.mail import EmailMultiAlternatives
from django.contrib import messages
from django.utils.translation import gettext as _
from django.template.loader import get_template

def send_email(subject, plain_template, html_template, context, to: List[str], attachments=None, request=None):
    try:
        plain_text = get_template(plain_template)
        html = get_template(html_template)
        text_content = plain_text.render(context)
        html_content = html.render(context)
        msg = EmailMultiAlternatives(subject, text_content, to=to, attachments=attachments)
        msg.mixed_subtype = 'related'
        msg.attach_alternative(html_content, "text/html")
        msg.send(fail_silently=True)
    except Exception as e:
        if request:
            messages.error(request, _('Ocurrió un error al enviar el correo electrónico.'))
        print(e)
        print(traceback.format_exc())

django-1          | Traceback (most recent call last):
django-1          |   File "/app/core/services.py", line 82, in send_email
django-1          |     msg.send(fail_silently=True)
django-1          |   File "/usr/local/lib/python3.12/site-packages/django/core/mail/message.py", line 307, in send
django-1          |     return self.get_connection(fail_silently).send_messages([self])
django-1          |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
django-1          |   File "/usr/local/lib/python3.12/site-packages/mailer/backend.py", line 12, in send_messages
django-1          |     messages = Message.objects.bulk_create([Message(email=email) for email in email_messages], MESSAGES_BATCH_SIZE)
django-1          |                                             ^^^^^^^^^^^^^^^^^^^^
django-1          |   File "/usr/local/lib/python3.12/site-packages/django/db/models/base.py", line 558, in __init__
django-1          |     _setattr(self, prop, value)
django-1          |   File "/usr/local/lib/python3.12/site-packages/mailer/models.py", line 148, in _set_email
django-1          |     self.message_data = email_to_db(val)
django-1          |                         ^^^^^^^^^^^^^^^^
django-1          |   File "/usr/local/lib/python3.12/site-packages/mailer/models.py", line 94, in email_to_db
django-1          |     return base64_encode(pickle.dumps(email)).decode("ascii")
django-1          |                          ^^^^^^^^^^^^^^^^^^^
django-1          | _pickle.PicklingError: Can't pickle <class 'django.core.mail.message.Alternative'>: attribute lookup Alternative on django.core.mail.message failed

[kevinrenskers]

Discussion in the Django forum: https://forum.djangoproject.com/t/django-5-2s-usage-of-named-tuples-in-emails-is-a-breaking-change/40586.

[kevinrenskers]

Django 5.2.1 will fix this regression and make emails pickleable again.

[tim-hub]

I think I got the same issue when sending html and text emails at the same time

[kevinrenskers]

Since Django 5.2.1 has been released I think we can safely close this issue.