TCP wrappers provide a way of implementing access controls by checking the address of a host requesting a particular network service against an access control list (ACL). Requests are granted or denied, accordingly. Besides providing this access control mechanism, TCP wrappers also log host requests for network services, which is a useful monitoring function. Examples of network services that might be placed under access control include rlogind, telnetd, and ftpd.
Starting with version 8.12, sendmail enables the use of TCP wrappers. This check does not bypass other security measures. By enabling TCP wrappers in sendmail, a check has been added to validate the source of a network request before the request is granted. See the hosts_access(4) man page.
For information about ACLs, see Using Access Control Lists to Protect UFS Files in Securing Files and Verifying File Integrity in Oracle Solaris 11.2 .