[kmail2] [Bug 451518] New: Use no or UTF-8 as default when non-ASCII characters are encountered in header

[Erik Quaeghebeur]

https://bugs.kde.org/show_bug.cgi?id=451518

            Bug ID: 451518
           Summary: Use no or UTF-8 as default when non-ASCII characters
                    are encountered in header
           Product: kmail2
           Version: 5.16.3
          Platform: Gentoo Packages
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: message list
          Assignee: kdepim-bugs at kde.org
          Reporter: bugs.kde.org at e3q.eu
  Target Milestone: ---

Created attachment 147503
  --> https://bugs.kde.org/attachment.cgi?id=147503&action=edit
mail with UTF-8 character in ASCII header

SUMMARY
When a mail with some non-ASCII characters is encountered with the encoding of
the header being (effectively) ASCII, KMail tries to decode it assuming
ISO-8859-1. Because currently such occurrences tend to actually be UTF-8, this
results in failed decodings in general. (I assume it was different in the past,
when ISO-8859-1 was the most common ASCII-extension encoding used.) Obviously,
the mail is malformed, because of the missing encoding information. So the
strict thing to do is to show explicitly that the character(s) cannot be
decoded, e.g., using the replacement character �. The lenient thing to do,
nowadays, is to assume UTF-8.

STEPS TO REPRODUCE
1. List folder with mail with non-encoded non-ISO-8895-1-character in header

OBSERVED RESULT
Observe that character is decoded as if it were ISO-8859-1

EXPECTED RESULT
Observe that character is decoded as replacement character � or as if it were
UTF-8.

SOFTWARE/OS VERSIONS
KMail: 5.18.3
KDE Plasma Version: 5.23.5
KDE Frameworks Version: 5.90.0
Qt Version: 5.15.2 (with https://community.kde.org/Qt5PatchCollection)

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