I have 50 here as well, but that seems a bit high. Maybe you can set it to 6.9 or something like that.
From the ISPConfig 3 Manual:
SPAM kill level: The system will trigger spam evasive actions (e.g. blocks mail) at that level. The value should be >= SPAM tag2 level. Decimal numbers are allowed. Important: if SPAM kill level = SPAM tag2 level, spam will be blocked and not delivered to the user's mailbox, so it doesn't make sense to specify a SPAM subject tag2.