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Cox Postmaster Administration

Learn how email administrators can improve deliverability rates to Cox Email and Cox Business Email users or troubleshoot email issues that may occur.

Cox recommends that all email administrators review the information below prior to contacting Cox regarding email deliverability issues.

Email Delivery Guidelines

Operating within these guidelines will improve delivery of your email.

  • Monitor real-time blacklists (RBL) listings for your IPs and domains. Cox uses several IP and domain-based RBLs to make filtering decisions. Ensuring that your IPs and domains are not listed on these types of lists will reduce your chances of being blocked by Cox as well as other providers.
  • Maintain DNS records for your IPs and domains. Cox requires that all sending IP addresses resolve to a valid reverse DNS entry. All sending domains must resolve to valid A or MX record. Connections from IPs or domains that do not have valid DNS entries will be rejected.
  • Ensure mailing lists contain valid recipients. Make sure that mailings are sent to valid recipients. Mail sent to a large number of invalid or non-existent recipients can result in the IP or domain being blocked.
  • Monitor your IP and domain reputation. Cox tracks the reputation of sending IPs and domains using data from spam complaints and spamtraps, as well as external reputation data sources. Maintaining a clean reputation will help minimize deliverability issues.
  • Investigate Simple Mail Transfer Protocol (SMTP) Rejection Messages. When a sender encounters either a temporary (4xx) or permanent (5xx) rejection, the error message will contain a code and information about the reason for the block. Please see the Error Codes section for more information about the possible errors that can be encountered.
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