当用虚拟用户aa@aa.com登录时，postfix却用aa和aa@linux.com来验证

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我的实验环境是：linux主机名为:apache.linux.com，后台管理用的是postfixadmin
现在用postfixadmin添加了一个aa.com虚拟域，新建用户为aa；查询mysql中存在该用户的记录
当用foxmail的pop3登陆时，提示“验证失败，请检查用户名和密码是否正确”
在maillog中的日志如下：
apache authdaemond: received auth request, service=pop3, authtype=login
Dec 15 04:01:21 apache authdaemond: authmysql: trying this module
Dec 15 04:01:21 apache authdaemond: received auth request, service=smtp, authtype=login
Dec 15 04:01:21 apache authdaemond: authmysql: trying this module
Dec 15 04:01:21 apache authdaemond: authmysqllib: connected. Versions: header 50088, client 50088, server 50088
Dec 15 04:01:21 apache authdaemond: SQL query: SELECT username, password, "", '1002', '1002', '/home/mail', maildir, "", name, "" FROM mailbox WHERE username = 'aa'
Dec 15 04:01:21 apache authdaemond: zero rows returned
Dec 15 04:01:21 apache authdaemond: no password available to compare
Dec 15 04:01:21 apache authdaemond: authmysql: REJECT - try next module
Dec 15 04:01:21 apache authdaemond: FAIL, all modules rejected
Dec 15 04:01:21 apache authdaemond: authmysqllib: connected. Versions: header 50088, client 50088, server 50088
Dec 15 04:01:21 apache authdaemond: SQL query: SELECT username, password, "", '1002', '1002', '/home/mail', maildir, "", name, "" FROM mailbox WHERE username = 'aa@linux.com'
Dec 15 04:01:21 apache authdaemond: zero rows returned
Dec 15 04:01:21 apache authdaemond: no password available to compare
Dec 15 04:01:21 apache authdaemond: authmysql: REJECT - try next module
Dec 15 04:01:21 apache authdaemond: FAIL, all modules rejected
Dec 15 04:01:21 apache postfix/smtpd[3118]: warning: unknown[192.168.8.240]: SASL LOGIN authentication failed: authentication failure
Dec 15 04:01:21 apache pop3d: LOGIN FAILED, user=aa, ip=[192.168.8.240]
Dec 15 04:01:21 apache postfix/smtpd[3118]: lost connection after AUTH from unknown[192.168.8.240]
Dec 15 04:01:21 apache postfix/smtpd[3118]: disconnect from unknown[192.168.8.240]
Dec 15 04:01:26 apache pop3d: Disconnected, ip=[192.168.8.240]
Dec 15 04:02:14 apache postfix/pickup[3089]: 9A50A44634: uid=0 from=<root>
Dec 15 04:02:14 apache postfix/cleanup[3124]: 9A50A44634: message-id=<20091215090214.9A50A44634@apache.linux.com>
Dec 15 04:02:14 apache postfix/qmgr[3040]: 9A50A44634: from=<root@linux.com>, size=2707, nrcpt=1 (queue active)
Dec 15 04:02:21 apache postfix/smtp[3482]: 9A50A44634: to=<root@linux.com>, orig_to=<root>, relay=smtp1.linux.com[140.211.169.67]:25, delay=7.2, delays=0.21/0.2/6.1/0.63, dsn=2.0.0, status=sent (250 2.0.0 nBF90olU027646 Message accepted for delivery)
Dec 15 04:02:21 apache postfix/qmgr[3040]: 9A50A44634: removed
Dec 15 04:04:41 apache postfix/anvil[3130]: statistics: max connection rate 1/60s for (smtp:192.168.8.240) at Dec 15 04:01:21
Dec 15 04:04:41 apache postfix/anvil[3130]: statistics: max connection count 1 for (smtp:192.168.8.240) at Dec 15 04:01:21
Dec 15 04:04:41 apache postfix/anvil[3130]: statistics: max cache size 1 at Dec 15 04:01:21

我看这是用aa@linux.com去查询的，而不是我的aa@aa.com,所以会出现这个验证失败的问题
请问：这个问题怎么解决，谢