There was a server ban? What for?
Backdoor way of limiting bandwidth usage. On TCP/IP, really a "server" is just the one that sends SYN|ACK packets in response to SYN packets, rather than sending out SYNs - but ISPs latched on to "no servers" as a more marketable way to kick heavy users off without being honest about usage limits.
With cable, downstream bandwidth is more abundant and more efficient (the upstream channel is vulnerable to collisions, since there are multiple senders on a channel) so heavy upload usage can actually be a problem to some extent. On ADSL and its derivatives, though, it's only your own link you're filling up with upstream traffic: the backhaul connections are invariably symmetric, so those gigabit+ links between you and the ISP are only full up in the other direction.
I switched back in 2012 from "unlimited" (but no servers, dynamic IP, ports blocked, sending nastygrams to anyone using "too much" of the "unlimited" bandwidth) to an ISP with actual explicit usage charges (and a small routed subnet with no ports blocked). As long as it's legal I can do what I want: mail servers, web servers, the lot - I just have to pay a bit more if I download more. (It's download traffic that matters to them: upstream, there's bandwidth to spare, because the links are symmetric.) I hated the idea of usage-based charging - but I hate all the other restrictions more; at about $0.30 per Gb, it's low enough not to bother me as much as "unlimited, but use it too much and we cut you off".