NAT is an interesting solution and we offer 20 ports which helps people still host websites, apps and services on our servers without needing a dedicated IPv4 address (reverse proxy).
We have IPv6 support, you just need to submit a ticket after ordering and we add 20 native IPv6 addresses!
We have a rate limited SMTP port and if people go over this we will give 1 warning, ask for the reason and if it's valid then we will either just let it continue or lift the limit. Repeated offences will have services terminated immediately. Same goes for copyright offences. The resources are fairly small (HDD/SSD, BW) so it is not too hard to detect.
You may be interested (since you appear to offer DNS Hosting) that many of these Mini plans are used as DNS slaves because of their cheap price. An interesting use I've found.