SUMMARY *** The option ShowUserAgent=true in kmail2rc section [Reader] does not work with any header (Vorspann). There is no result though the source code of the email contains X-Mailer. *** SOFTWARE/OS VERSIONS Operating System: openSUSE Tumbleweed 20220110 KDE Plasma Version: 5.23.4 KDE Frameworks Version: 5.89.0 Qt Version: 5.15.2 Kernel Version: 5.15.12-1-default (64-bit) Graphics Platform: X11 Processors: 16 × 11th Gen Intel® Core™ i7-11700F @ 2.50GHz Memory: 30.8 GiB of RAM Graphics Processor: NVIDIA GeForce RTX 3060/PCIe/SSE2ADDITIONAL INFORMATION KMAIL: 5.19.0 (21.12.0)
it seems that it's an old/remove settings. As it's not supported in source code
Git commit fc0b487d3f3ac9c9ca0650aa635795b5478de85b by Laurent Montel. Committed on 16/12/2022 at 06:28. Pushed by mlaurent into branch 'release/22.12'. Remove info about removed feature (ShowUserAgent) M +0 -17 doc/kmail2/configure.docbook https://invent.kde.org/pim/kmail/commit/fc0b487d3f3ac9c9ca0650aa635795b5478de85b
This feature was removed long time ago. I close this bug.