This!  Yes, please!  This is desperately needed.  Afrinic servers are spewing spam, phish, spear phish, script attack, and other malicious emails, and there's no way to identify them except by a wide range of IPs in the headers.

I'm bumping this because I would love this to be a feature (with a drop-down for the CIDR Range, i.e. /24, /23, /22, etc.). Granted I can manually enter them into the Blacklist as such, but most of the time when I need to block IPs from the Inbound Senders it is after-hours and I'm on my phone at the pub. It's a QOL feature request, but it would be very much welcomed.