There seems to be a bug in the user interface for the email users when administrating email filter rules in ISPConfig3. ISPConfig version 18.104.22.168 Log in as an email user in ISPConfig3 control panel (i.e. use email address and email account password), create a number of email filter rules, making more rules than what fits in one page. It is not possible to switch from page 1 of the email filter rules, i.e. the navigator under the email filter rules doesn't work. If logged in as administrator, it is possible to see all pages of the email filter rules for the user. So the problem is only present when one is logged in as an email user.