postfix、dovecot、mysql、postfixadmin虚拟用户收不到邮件！

系统版本：Centos 6.9

域名942sh.com在阿里云注册并做好解析，能正常访问，能正常发外部邮件。但就是收不到邮件。邮件目录设置为 /home/vmail/域名/虚拟用户/Maildir/

用163邮件给本域发邮件，会返回错误邮件：

This is the mail system at host mail.942sh.com.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

               The mail system

<abcccy@942sh.com>: unknown user: "abcccy"

以下为dovecot日志：

dovecot_info.log

Nov 17 23:38:04 auth: Info: pam(caoyao@942sh.com,218.17.68.243): unknown user
Nov 17 23:38:04 auth: Info: passwd(caoyao@942sh.com,218.17.68.243): unknown user
Nov 17 23:38:04 pop3-login: Info: Login: user=<caoyao@942sh.com>, method=PLAIN, rip=218.17.68.243, lip=192.168.14.178, mpid=21617
Nov 17 23:38:04 pop3(caoyao@942sh.com): Info: Disconnected: Logged out top=0/0, retr=0/0, del=0/0, size=0
Nov 17 23:38:44 auth: Info: pam(caoyao@942sh.com,218.17.68.243): unknown user
Nov 17 23:38:44 auth: Info: passwd(caoyao@942sh.com,218.17.68.243): unknown user
Nov 17 23:38:44 pop3-login: Info: Login: user=<caoyao@942sh.com>, method=PLAIN, rip=218.17.68.243, lip=192.168.14.178, mpid=22059
Nov 17 23:38:44 pop3(caoyao@942sh.com): Info: Disconnected: Logged out top=0/0, retr=0/0, del=0/0, size=0

日志中一直提示：unknown user，不知道是什么原因。

dovecot_debug.log

Nov 17 23:38:02 auth: Debug: client in: AUTH
1
PLAIN
service=pop3
lip=192.168.14.178
rip=218.17.68.243 lport=110
rport=7307
resp=AGNhb3lhb0A5NDJzaC5jb20AZ21hZnRraHRkNDg2Mjk2Mw==
Nov 17 23:38:02 auth: Debug: pam(caoyao@942sh.com,218.17.68.243): lookup service=dovecot
Nov 17 23:38:02 auth: Debug: pam(caoyao@942sh.com,218.17.68.243): #1/1 style=1 msg=Password:
Nov 17 23:38:04 auth: Debug: sql(caoyao@942sh.com,218.17.68.243): query: SELECT username AS user,password FROM mailbox WHERE username = 'caoyao@942sh.com' AND active='1'
Nov 17 23:38:04 auth: Debug: client out: OK
1
user=caoyao@942sh.com
Nov 17 23:38:04 auth: Debug: master in: REQUEST
3235119105
20942
1
6773b0533d8b4bd7b7bd952cf3b81b25
Nov 17 23:38:04 auth: Debug: passwd(caoyao@942sh.com,218.17.68.243): lookup
Nov 17 23:38:04 auth: Debug: master out: USER
3235119105
caoyao@942sh.com
uid=5000
gid=5000
home=/home/vmail/942sh.com/caoyao
Nov 17 23:38:04 pop3(caoyao@942sh.com): Debug: Effective uid=5000, gid=5000, home=/home/vmail/942sh.com/caoyao
Nov 17 23:38:04 pop3(caoyao@942sh.com): Debug: maildir++: root=/home/vmail/942sh.com/caoyao/Maildir, index=, control=, inbox=/home/vmail/942sh.com/caoyao/Maildir
Nov 17 23:38:41 auth: Debug: auth client connected (pid=22057)
Nov 17 23:38:41 auth: Debug: client in: AUTH
1
PLAIN
service=pop3
lip=192.168.14.178
rip=218.17.68.243 lport=110
rport=7407
resp=AGNhb3lhb0A5NDJzaC5jb20AZ21hZnRraHRkNDg2Mjk2Mw==
Nov 17 23:38:41 auth: Debug: pam(caoyao@942sh.com,218.17.68.243): lookup service=dovecot
Nov 17 23:38:41 auth: Debug: pam(caoyao@942sh.com,218.17.68.243): #1/1 style=1 msg=Password:
Nov 17 23:38:44 auth: Debug: sql(caoyao@942sh.com,218.17.68.243): query: SELECT username AS user,password FROM mailbox WHERE username = 'caoyao@942sh.com' AND active='1'
Nov 17 23:38:44 auth: Debug: client out: OK
1
user=caoyao@942sh.com
Nov 17 23:38:44 auth: Debug: auth client connected (pid=22058)
Nov 17 23:38:44 auth: Debug: master in: REQUEST
838860801
22057
1
de52cb9ce0e77ba34d67c89e0a7a4b76
Nov 17 23:38:44 auth: Debug: passwd(caoyao@942sh.com,218.17.68.243): lookup
Nov 17 23:38:44 auth: Debug: master out: USER
838860801
caoyao@942sh.com
uid=5000
gid=5000
home=/home/vmail/942sh.com/caoyao
Nov 17 23:38:44 pop3(caoyao@942sh.com): Debug: Effective uid=5000, gid=5000, home=/home/vmail/942sh.com/caoyao
Nov 17 23:38:44 pop3(caoyao@942sh.com): Debug: maildir++: root=/home/vmail/942sh.com/caoyao/Maildir, index=, control=, inbox=/home/vmail/942sh.com/caoyao/Maildir