[exim] Outlook and Exim filter

Hi.

I have a filter likes this in /etc/system_filter.exim file

if
  $h_to: is "all@???"
then
    if $sender_address: does not match "(user1|user2|user3)@mydomain.com"
        then
                fail text "You are not in the allowed list"
                seen finish
        endif
endif

It works well with emails sending from webmail, or other email
clients. But with Outlook, all emails can pass the filter, and be
processed as a normal message. It looks like Exim and Outlook don't
match headers, or something like that?

Any ideas?

Thank you.