Bug 451518

Summary: Use no or UTF-8 as default when non-ASCII characters are encountered in header
Product: [Applications] kmail2 Reporter: Erik Quaeghebeur <bugs.kde.org>
Component: message listAssignee: kdepim bugs <pim-bugs-null>
Status: REPORTED ---    
Severity: normal    
Priority: NOR    
Version First Reported In: 5.16.3   
Target Milestone: ---   
Platform: Gentoo Packages   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: mail with UTF-8 character in ASCII header

Description Erik Quaeghebeur 2022-03-15 08:23:37 UTC 
Created attachment 147503 [details]
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)