[kmailtransport] [Bug 476480] New: KMail/Akonadi applies Unicode compatibility decomposition to sender and recipient names before sending

[Yuki Schlarb]

https://bugs.kde.org/show_bug.cgi?id=476480

            Bug ID: 476480
           Summary: KMail/Akonadi applies Unicode compatibility
                    decomposition to sender and recipient names before
                    sending
    Classification: Applications
           Product: kmailtransport
           Version: unspecified
          Platform: Debian unstable
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: kdepim-bugs at kde.org
          Reporter: erin-kde at ninetailed.ninja
  Target Milestone: ---

SUMMARY
When changing my identity settings KMail settings to make use of U+2004
(THREE-PER-EM SPACE / thick space) and U+2009 (THIN SPACE) to visually separate
the parts of my name I noticed that KMail shows these correctly in settings and
composer, but the actually sent messages instead use U+0020 (ASCII SPACE).
While I have not verified this in the source code I’m almost certain this is
due to KMail/Akonadi/KMailTransport applying Unicode compatibility
decomposition (NFKC normalization) before encoding the sender and recipient
names.

GitHub at least doesn’t seem to have any problems encoding these correctly and
they are displayed correctly in KMail in messages received from it. Python’s
`email.header` appears to encode it basically the same way.

In particular for the name “First Collective Last” (using the mentioned U+2004
and U+2009), the three tested implements yield:
  1. KMail/Akonadi/KMailTransport: “From: First Collective Last
<email-address>”  (using just ASCII spaces everywhere)
  2. GitHub: “From: =?UTF-8?b?Rmlyc3TigIRDb2xsZWN0aXZl4oCJTGFzdA==?=
<notifications at github.com>”
  3. Python `email.header`: “From:
=?utf-8?b?Rmlyc3TigIRDb2xsZWN0aXZl4oCJTGFzdA==?= <email-address>“

STEPS TO REPRODUCE
1. Compose an email to “First Collective Last <some-email-address-of-yours>”
(copy-paste it!) in KMail – replacing the address as intended

OBSERVED RESULT
The received message has the fancy spaces replaced with the plain ASCII ones
and hence contains a “To: First Collective Last <some-email-address-of-yours>”
as a header, discarding the extra information originally entered

EXPECTED RESULT
The fancy quotes should remain and be encoded instead.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Debian unstable
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.104.0
Qt Version: 5.15.8

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