Bug 455190

Created attachment 149646 [details]
KMail output after opening the mail

SUMMARY
***
NOTE: If you are reporting a crash, please try to attach a backtrace with debug symbols.
See https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports
***

STEPS TO REPRODUCE
1. Receive a S/MIME signed & encrypted mail (with attachments, encrypted mail with attachments is ~20 KiB big, and probably sent from Microsoft Outlook)
2. Try to encrypt it

OBSERVED RESULT
KMail takes a few seconds "to verify the signature of the mail" after clicking on "decrypt" (I disabled auto-decrypting due to various reasons), then the mail content pops up (correctly, with no issues, but no attachments displayed in the header) with a green background (meaning mail is authentic) for around 100 ms, then the message preview window is completely blank (in the background color of the theme). This stays for around 3 seconds, then the whole process seems to repeat without user interaction. Trying to interact with KMail while the preview window is empty for 3 seconds shows that the UI is freezing, e.g. if then trying to switch to another mail first happens after KMail seems "finished with hanging". After opening the mail, while watching the process repeating, it outputs a few lines, but multiple repeating times, consecutive to what is happening in the UI (view attached log file; the last few lines might be output produced while switching to another mail, which is then displayed fine). Most notably is the line:
org.kde.pim.mimetreeparser: unknown mimetype "application/x-pkcs7-mime"

Thunderbird with its integrated support for S/MIME has no problems opening the same mail.

EXPECTED RESULT
KMail displays the mail and it's content properly without retrying anything.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Debian testing (Kernel: 5.17.0-1-amd64)
(available in About System)
KDE Plasma Version: 5.24.5
KDE Frameworks Version: 5.94.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION

I am not sure what causes this bug. This is the first & only mail so far, which seems to be a problem to KMail. The multiple error messages KMail outputs to stderr seems unique (at least no search engine I tried found anyone else with a similar one).
I can share more diagnostic information about the mail but not disclosure the mail itself.