USA.net does not publish either connection or sending limits.
USA.net does provide a postmaster website for senders.
USA.net does provide a feedback loop.
USA.net does not provide a whitelist for senders.
USA.net uses the Return Path Certified whitelist in mail delivery decisions. Mail from IPs on the Return Path Certified list will see better delivery at USA.net.
USA.net provides an IP lookup form on their postmaster site. They do not provide any public contact paths.
USA.net started using Cloudmark products to filter mail in early 2010. 1