The script works nice, exactly like described. No special bonuses. Also it's a bit annoying that clicking somewhere in the subject column also selects a message.
For the rest anything works fine, although I would appreciate it if you would add Solcon Webmail to the script:
// @include https://webmail.solcon.nl/src/right_main.php
// @include https://webmail.solcon.nl/src/right_main.php?*