解决方法 ：

1

[root@email roundcubemail-0.7]# pwd 
/var/www/roundcubemail-0.7
[root@email roundcubemail-0.7]# cd plugins/password/
config.inc.php       drivers/             package.xml          password.php         
config.inc.php.dist  localization/        password.js          README               
[root@email roundcubemail-0.7]# cd plugins/password/
[root@email password]# 

2

[root@email password]# vim config.inc.php

3

将这一行

#$rcmail_config['password_db_dsn'] = "mysqli://roundcube:Kwnw3mjWrWWjI6O5qsOmHI0pI6n8hW@127.0.0.1/vmail";

修改成这样

$rcmail_config['password_db_dsn'] = "mysql://root:root@127.0.0.1/vmail";

root:root  表示   用户名：密码

保存即可。。