#25986: Django crashes on unicode characters in the local part of an e-mail
address
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Reporter: Sergei Maertens | Owner: Sergei
| Maertens
Type: Bug | Status: closed
Component: Core (Mail) | Version: 1.9
Severity: Normal | Resolution: fixed
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Mike Edmunds):
Does anyone know of an email server or service where this sort of non-
ASCII mailbox works?
Sorry to unearth this ancient ticket. I'm hoping one of the original
participants or cc's might have more info.
This ticket attempted to add support for non-ASCII characters in the local
part (username) of an email address: e.g., `j.lóp...@example.com` . But the
implementation used an RFC 2047 encoded-word
(`=?utf-8?b?ai5sw7NwZXo=?=@example.com`). RFC 2047 specifically prohibits
that in an addr-spec (email address). And I've been unable to find any
email systems that actually support this behavior. At best, the message
bounces—and sometimes it just disappears without a trace.
If anyone has an example where RFC 2047 encoded-word email addresses work,
I'll put some effort into preserving the current behavior as part of
updating to Python's modern email API (#35581). Or if nobody is actually
using this successfully, I'm going to treat it as a bug.
More info:
*
[https://datatracker.ietf.org/doc/html/rfc2047#section-5:~:text=An%20%27encoded%2Dword%27%20MUST%20NOT%20appear%20in%20any%20portion%20of%20an%20%27addr%2Dspec%27.
RFC 2047 section 5(3)] specifies that: "An 'encoded-word' MUST NOT appear
in any portion of an 'addr-spec'." (And I can't find any later RFC that
removes this restriction.)
* I can't find any email software or services that support RFC 2047 in an
email localpart. The closest is Exim, which can [https://www.exim.org
/exim-html-current/doc/html/spec_html/ch-internationalisation.html convert
a localpart to/from an A-Label] (an
[https://datatracker.ietf.org/doc/html/rfc5891 RFC 5891] IDNA encoding,
a.k.a. "punycode": `j.xn--lpez-...@example.com`). But that's a different
encoding, and this behavior seems to be unique to Exim.
* From what I can tell, the only spec compliant way to use a non-ASCII
localpart involves keeping utf-8 un-encoded in the headers, and then
sending with the SMTPUTF8 extension
([https://datatracker.ietf.org/doc/html/rfc6530.html RFC 6530] /
[https://datatracker.ietf.org/doc/html/rfc6531.html RFC 6531] /
[https://datatracker.ietf.org/doc/html/rfc6532.html RFC 6532]). There
doesn't seem to be any spec that allows a non-ASCII localpart with 7-bit
header encoding.
* The Python behavior seems to be a bug. Note that the same Python code
also converts a non-ASCII domain name to an RFC 2047 encoded-word, which
is definitely not deliverable: `juan@lópez.example.mx` →
`juan@=?utf-8?q?l=C3=B3pez?=.example.mx`. This is an
[https://github.com/python/cpython/issues/83938#issuecomment-1093859100
acknowledged bug] in Python's email package.
(Incidentally, RFC 2047 encoded words ''are'' allowed in a ''display-
name'': `J. López <jlo...@example.com>` → `J. =?utf-8?q?L=C3=B3pez?=
<jlo...@example.com>`. That worked before and after this ticket, and won't
be changed by #35581.)
--
Ticket URL: <https://code.djangoproject.com/ticket/25986#comment:12>
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