If the user has a large number of email account, accessing user panel -> email account (list email) will loading forever
In my case, user with 80 email account already got this problem
seem someone already found this problem since last year :-)
https://forum.centos-webpanel.com/index.php?topic=7899.0
This link will help to add/del/edit user/alias till problem sorted out
https://forum.centos-webpanel.com/index.php?topic=6631.0