To block these serverwide or on a per-user basis, you may do so
by editing the blacklist settings. To block email from a particular
country, you may use the pattern of ‘*@*.<CCtld>’. To block a
specific domain, you would use ‘*@*.<tld>’. For instance, if you
wanted to block all mail from Taiwan, you would use ‘*@*.tw’. Or
to block all mail from mydomain.com, you would use ‘*@*.mydomain.com’.