With an IMAP account and "preferences/Advanced/Move deleted mails to trash and expunge immediately" not set, the user has to manually expunge deleted mails by invoking a menu item in the tools menu for each folder that contains mails marked for deletion (unless the IMAP server expunges mails on its own, which some servers apparently do). Suggestion: Include an option to automatically expunge all mails marked for deletion when exiting the client.