Net Neutrality doesn't prevent network operators from stopping malicious activity on their network.
Blocking Port 25 to specific providers unless they pay up would be a problem, but blocking port 25 globally (except, say, to their own SMTP servers) is perfectly okay.
Blocking Port 25 to specific providers unless they pay up would be a problem, but blocking port 25 globally (except, say, to their own SMTP servers) is perfectly okay.