Currently do to excessive abuse we block the following IP ranges available at the below URLs.
http://www.okean.com/sinokoreacidr.txt
https://www.countryipblocks.net/e_country_data/JP_cidr.txt
This is all CN, KR, and JP net-blocks.
Currently on the smtp auth port 587 we are blocking all IPs outside of US due to login attempts from unknown sources.