邮件应用中可能回又如下的应用需求：
某销售A只能收到来自163.com及sina.com的邮件某技术员B只能给内部用户发邮件，不允许向外网发邮件，但可以收到外网邮件某主管可以收发内、外网邮件......
Hello!
I have the same problem:
1. I need to permit some internal users (not all) to send mail to any
external user (Internet)
2. I need to permite any external user to send mail to some my internal
users (not all)
In fact, the problem is: just "some" of my internal users have permission to
receive mail from and send mail to the Internet.
How can I solve this?
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新闻群组：mailing.postfix.users
日期：2002-12-04 15:18:04 PST
In the example below, the same list of restricted_users is used for
controlling both who can send and who can receive internet mail. If you
don't require the local_plus feature, just leave that part out.
in main.cf:
use restriction classes to make restricted_users file more readable.
smtpd_restriction_classes = local_only, local_plus
local_only =
reject_unauth_destination
permit_mynetworks
reject
local_plus =
check_recipient_access hash:/etc/postfix/local_plus
check_sender_access hash:/etc/postfix/local_plus
reject_unauth_destination
permit_mynetworks
reject
this is the default setting, required for this setup.
smtpd_delay_reject = yes
we'll do this in sender restrictions to avoid open relay problems.
smtpd_sender_restrictions =
check_sender_access hash:/etc/postfix/restricted_users
check_recipient_access hash:/etc/postfix/restricted_users
and in /etc/postfix/restricted_users
# /etc/postfix/restricted_users
# this file contains a list of users only allowed to send and receive local
mail
# postmap this file after changes
# local users not listed here have no restrictions
user1@miodemi.com local_only
user2@miodemi.com local_plus
and in /etc/postfix/local_plus:
# /etc/postfix/local_plus
# this file contains allowed destinations and senders
# for users restricted to local_plus
# postmap this file after changes
miproveedor.com OK
Remember to "postmap local_plus" and "postmap restricted_users" after
making changes to them.
Remember to run "postfix reload" after changing main.cf
hzqbbc的限制方法（转自hzqbbc的blog）
有几个方法：
1) smtpd_restriction_classes = local_only
设置一个限制类别叫local_only，然后参考access(5)的格式做一个访问控制：
local_only = check_recipient_access hash:/etc/postfix/maps/my_rcpt
文件my_rcpt内容：
163.com RELAY21cn.com RELAYhzqbbc.com RELAY
然后，设置：
smtpd_sender_restrictions = check_sender_access hash:/etc/postfix/maps/mysender
mysender内容：
hzqbbc@local.hzqbbc.com local_only
这样凡是Mail from:
按这个方法，还可以设置更多的类别，例如remote_only以及不限制的帐号等。但这些都只对from:限制。而且不管是否SASL后的。所以有一定缺陷。不过，已经达到目的了。
2)使用snapshot版的policy策略
根据某个hash表或配置文件，判断对应的sender和recipient是否匹配，匹配就返回OK或者DUNNO或者RELAY等（可能RELAY已经过时，这个是postfix 1.1.x的）如果不匹配就返回错误代码
按postfix所带的smtpd-policy.pl模式，修改一下就可以使用了。详细参考POLICY_README等。
我自己的例子：
1)定义类send2hrall：
smtpd_restriction_classes = send2hrall
send2hrall =
check_sender_access mysql:/usr/local/etc/postfix/mysql-send2hrall.cf,reject
配置文件 send2hrall.cf内容如下：
hosts = localhost
user = mailuser
password = mailpasswd
dbname = maildatabase
query = select access from mysql-send2hrall where source = '%s'
`id` int(11) unsigned NOT NULL auto_increment,
`ctime` int(11) unsigned default NULL,
`source` varchar(128) NOT NULL default '',
`access` varchar(16) NOT NULL default '',
`type` char(1) NOT NULL default 'S',
PRIMARY KEY (`id`),
KEY `source` (`source`,`type`,`access`,`ctime`)
) ENGINE=MyISAM AUTO_INCREMENT=12 DEFAULT CHARSET=gb2312;
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