Thanks Till for your help. It's good now.
Here is what I did:
In the config.php of the plugin change_sqlpass, I set the following variables as followed:
$csp_dsn = 'mysql://dbuser:dbuser_pass@localhost/ISPConfigDB';
is the user who has access to the ISPConfig database ISPConfigDB. Replace ISPConfigDB with the name of your ISPConfig database (dbispconfig by default) and dbuser_pass
with the user password.
$lookup_password_query = 'SELECT count(*) FROM mail_user WHERE email = "%1" AND password = %4';
where mail_user is the table used by ISPConfig3 and email and password are the columns in that table.
$password_update_queries = array('UPDATE mail_user SET password = %4 WHERE email = "%1"');
$password_encryption = 'MYSQLENCRYPT';
Till, I know you said to use MD5CRYPT but it did not work for me. When I used it, the password I enter on the change password form as my old password could not be matched with the one in the database.
$csp_salt_static = 'LEFT(password, 12)';
That worked for me.