Bug 430719

SUMMARY
Dear Maintainer,

when opening emails in windows on their own the next email has to opened by
closing the current window, selecting the next one in the folder and opening it
in another window. It would be desirable to be able to navigate through email
from within the email window.
Fun fact, this was an unanswered question on stackexchange 4 years and 9
mtónths ago: https://unix.stackexchange.com/questions/259812/next-unread-
message-shortcut-in-kmail-message-window

This is amplified by kmail's misbehaviour on KDE Wayland. Through the inability
to show the email in the preview pane, emails have to be opened in email
message windows on Wayland (see https://bugs.kde.org/show_bug.cgi?id=414955)

STEPS TO REPRODUCE
1. Open an email in a window of its own
2. To open the next, previous,... email there is no button

OBSERVED RESULT
No button or shortcut to switch to the next, previous, ...

EXPECTED RESULT
A convenient way to move between emails inside a folder without having to close the email window

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.19.5
KDE Frameworks Version: 5.74.0
Qt Version: 5.15.2