SUMMARY
If the "Reply or forward using the same visual format as the original message (plain text or HTML)" option is selected, the Kmail will hang while replying to HTML mail. It will also raise the CPU load to 100%.


STEPS TO REPRODUCE
1. go to settings, composer and select the option, click Apply / OK
2. select HTML mail
3. press R or A

OBSERVED RESULT
CPU load jumps to 100%, the composer window is not opened, and Kmail stops responding.

EXPECTED RESULT
Composer window to open.

SOFTWARE/OS VERSIONS
Operating System: Artix Linux x86_64
KDE Plasma Version: 6.0.2
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Kernel Version: 6.8.1-artix1-1 (64-bit)
Graphics Platform: Wayland
Processors: 24 × AMD Ryzen 9 5900X 12-Core Processor
Memory: 62,7 GiB of RAM
Graphics Processor: AMD Radeon RX 6700 XT

ADDITIONAL INFORMATION
The last strace entries:

openat(AT_FDCWD, "/usr/lib/aspell-0.60/en-wo_accents-only.rws", O_RDONLY) = 115
fstat(115, {st_mode=S_IFREG|0644, st_size=176080, ...}) = 0
read(115, "aspell default speller rowl 1.10"..., 4096) = 4096
newfstatat(AT_FDCWD, "/usr/lib/aspell-0.60/en-wo_accents-only.rws", {st_mode=S_IFREG|0644, st_size=176080, ...}, 0) = 0
close(115)                              = 0
read(114, "", 4096)                     = 0
close(114)                              = 0
close(113)                              = 0
read(111, "", 4096)                     = 0
close(111)                              = 0
close(24)                               = 0
newfstatat(AT_FDCWD, "/home/canny/.aspell.en.pws", 0x7ffed824d640, 0) = -1 ENOENT (No such file or directory)
access("/home/canny/.aspell.en.pws", F_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/home/canny/.aspell.en.per", O_RDONLY) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, "/home/canny/.aspell.en.prepl", 0x7ffed824d640, 0) = -1 ENOENT (No such file or directory)
access("/home/canny/.aspell.en.prepl", F_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/home/canny/.aspell.en.rpl", O_RDONLY) = -1 ENOENT (No such file or directory)
access("cid:image001.png@01DA81C0.33A3AEC0", F_OK) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, "/etc/localtime", {st_mode=S_IFREG|0644, st_size=1920, ...}, 0) = 0
newfstatat(AT_FDCWD, "/etc/localtime", {st_mode=S_IFREG|0644, st_size=1920, ...}, 0) = 0
openat(AT_FDCWD, "/usr/local/share/fonts/WindowsFonts/calibri.ttf", O_RDONLY) = 24
fcntl(24, F_SETFD, FD_CLOEXEC)          = 0
fstat(24, {st_mode=S_IFREG|0644, st_size=1648120, ...}) = 0
mmap(NULL, 1648120, PROT_READ, MAP_PRIVATE, 24, 0) = 0x74bce7e6d000
close(24)                               = 0
write(5, "\1\0\0\0\0\0\0\0", 8)         = 8
write(5, "\1\0\0\0\0\0\0\0", 8)         = 8
brk(0x6435fc91b000)                     = 0x6435fc91b000
brk(0x6435fcd1b000)                     = 0x6435fcd1b000
brk(0x6435fd31b000)                     = 0x6435fd31b000
mmap(NULL, 16781312, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x74bc7ae00000
mremap(0x74bc7ae00000, 16781312, 33558528, MREMAP_MAYMOVE) = 0x74bc78c00000
mremap(0x74bc78c00000, 33558528, 67112960, MREMAP_MAYMOVE) = 0x74bb9fe00000
mremap(0x74bb9fe00000, 67112960, 134217728, MREMAP_MAYMOVE) = 0x74bb97e00000
mremap(0x74bb97e00000, 134217728, 268439552, MREMAP_MAYMOVE) = 0x74bb87c00000
mremap(0x74bb87c00000, 268439552, 536875008, MREMAP_MAYMOVE) = 0x74bb67a00000
mremap(0x74bb67a00000, 536875008, 1073741824, MREMAP_MAYMOVE) = 0x74bb27a00000
mremap(0x74bb27a00000, 1073741824, 2147487744, MREMAP_MAYMOVE) = 0x74baa7800000
mremap(0x74baa7800000, 2147487744, 4294967296, MREMAP_MAYMOVE) = 0x74b9a7800000
mremap(0x74b9a7800000, 4294967296, 8589934592, MREMAP_MAYMOVE) = 0x74b7a7800000
mremap(0x74b7a7800000, 8589934592, 17179873280, MREMAP_MAYMOVE) = 0x74b3a7600000
mremap(0x74b3a7600000, 17179873280, 34359742464, MREMAP_MAYMOVE) = 0x74aba7400000
mremap(0x74aba7400000, 34359742464, 68719480832, MREMAP_MAYMOVE) = 0x749ba7200000
+++ killed by SIGKILL +++