Since "US MAILACCESS.txt" is not a recognized formal standard, it likely refers to a local technical configuration file or a draft document for an internal or Simple Mail Transfer Protocol (SMTP) implementation.
IP ranges and domains permitted for direct relay. US MAILACCESS.txt
This draft assumes familiarity with ARPA standard mail formats (RFC 5321/5322). It is intended to be used in conjunction with localized firewall rules to restrict access to proprietary mail servers, especially for systems that require specific restricted IP source addresses or browser-based logins. Since "US MAILACCESS
Support for secure handshake protocols, ensuring that only authenticated clients can query the mail store. US MAILACCESS.txt