[Django] #37167: (Officially) allow Address objects as email addresses

[Django]

#37167: (Officially) allow Address objects as email addresses
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Reporter: Mike | Owner: Mike Edmunds
Edmunds |
Type: | Status: assigned
Cleanup/optimization |
Component: Core | Version: 6.0
(Mail) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Django should officially support Python `email.headerregistry.Address`
objects in django.core.mail functions and the `ADMINS`, `MANAGERS`,
`DEFAULT_FROM_EMAIL`, and `SERVER_EMAIL` settings.

This actually works now (for everything except `ADMINS` and `MANAGERS`),
but isn't officially documented or tested. (And it ''would'' work for
`ADMINS` and `MANAGERS` except that they specifically reject any non-`str`
values to help avoid config errors.)

Forum request: https://forum.djangoproject.com/t/ticket-34753-document-
how-to-properly-escape-to-in-email-messages/43551/10.

== Background

Python's
[https://docs.python.org/3/library/email.headerregistry.html#email.headerregistry.Address
email.headerregistry.Address] object can be used to compose an email
address from parts (a `display_name` and `addr_spec` or `username` and
`domain`). And for security, it ''should'' be used when building an email
address from user-supplied parts (see #34753 and
[https://github.com/django/django/pull/21467 PR #21467]).

Python's `EmailMessage` class accepts `Address` objects in all address
headers. You can a set a message's "From" header to an `Address`, or its
"Cc" header to a list of `Address` objects. (You can also set a "Date"
header to a `datetime` object, etc.)

Django's `EmailMessage` class accidentally supports `Address` objects, in
all headers since 6.0 and in all but "From" since at least 5.2 (maybe
earlier). It currently converts the address objects to strings, and then
Python parses them back into address objects.

== Proposal

* Update the `ADMINS` and `MANAGERS` recipient-type check in
`django.core.mail._send_server_message()` to allow `Address`.
* Change `EmailMessage.message()` and `_set_list_header_if_not_empty()` to
avoid casting an `Address` to a `str` just so Python can parse it back
again. (The cast is there primarily for lazy strings.)
* Add tests!
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Ticket URL: <https://code.djangoproject.com/ticket/37167>
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