E-mail filtering blocks all e-mail

Hi,

One of my customers has repeatedly a problem with e-mail filtering.

His filter settings look like this:

Filter Destination
$ "" Discard
$header_subject: contains " IST " Discard
$header_subject: contains "***SPAM***" Discard
...​

The first line blocks all e-mails. When I delete this line, it automatically comes back after a while.

Anyone who knows how to delete it permanent?

Thanks,
Bart