Cox provides high speed network access as well as mailboxes for their subscribers.
Delivering to Cox
Cox throttles mail based on sender reputation, both IP based and domain based. Senders are limited to opening 5 connections per IP address . They also have a published limit of 100 messages per connection. In addition to those limits, Cox will throttle based on sender reputation.
Cox requires valid reverse DNS on all sending IPs. All sending domains must have a valid A or MX record.
Some business domains are hosted by Cox, but they do not offer general hosting. Email addresses in the cox.net domain belong to subscribers, addresses in the cox.com domain are reserved for Cox employees. This page discusses filtering and limits on the cox.net email addresses.
Important links and references
Cox has an extensive set of postmaster pages providing information about delivering mail to cox.net email addresses.
There is a feedback loop for cox.net email addresses. The FBL is administered by Return Path. Applications are accepted at the Cox FBL signup page. IP addresses will only be accepted if their SenderScore is above 60 or if their SenderScore is between 30 and 60 and the IP does not appear on any DNSBLs. IP addresses with a SenderScore below 30 will not be accepted.
Cox does not offer whitelisting services.
Cox uses the Return Path Certified whitelist in mail delivery decisions. Mail from IPs on the Return Path Certified list will see better delivery at Cox domains.
Support for Senders
As part of their postmaster webpages, they maintain a comprehensive list of error codes returned in response to blocked email. They also provide a blocklist removal form. Cox does not provide any formal way to contact them directly.
Cox uses a number of commercial spam filters and spamfiltering services. For IP filtering Cox is using Spamhaus Zen, the Return Path DNSBL, the Invaluement SIP list, and Cloudmark CSI. Cox is also using multiple lists for domain based filtering, including SURBL, Spamhaus DBL, and the Invaluement URI list.