Since around December 2016 NIS (v22.9.0.71) no longer detects any spam in my POP3 account. I use Thunderbird as an email client. NIS settings say that antispam is on, port 110 is protected, but no message gets flagged, however obvious the spam.
System is Windows 10 Pro 1607 64bit.
Thunderbird does no support integration with NIS, but the POP3 port should still be monitored.