sendmail

/etc/mail/access

The table itself uses e-mail addresses, domain names, and network
numbers as keys.  Note that IPv6 addresses must be prefaced with "IPv6:".
For example,

        From:spammer@aol.com                    REJECT
        From:cyberspammer.com                   REJECT
        Connect:cyberspammer.com                REJECT
        Connect:TLD                             REJECT
        Connect:192.168.212                     REJECT