For all mails transfered in Junk-E-Mail-folder - by rule or by mouse-click - should be a possibility to delete them by a rule after x days.
You can right-click at Junk folder and then choose Empty Junk Folder. We also plan to implement emptying junk folder on exit in one of next versions.
The right-click was well-known, the second was and is my request. Hopefully in the next version.