function filter_var missing
Ubuntu 16.04 php7
When trying to change or create a new mailbox, the following error occurs:
function filter_var missing
/usr/local/ispconfig/interface/lib/classes/tform_base.inc.php
line 1015
if(function_exists('filter_var') && $field_value < 2147483647) {
This checks that causes the error: "$field_value < 2147483647"